Vocabulary and Executive Functioning: A Scoping Review of the Unidirectional and Bidirectional Associations across Early Childhood Free

When considering the many skills acquired across the span of early childhood, language and executive functioning (EF) abilities are among the earliest to emerge and are in many ways foundational to later development. Both language and EF are predictive of later academic achievement and social competence (Blair & Razza, 2007; Moll et al., 2015). In particular, the acquisition of proficient number skills as well as reading comprehension, interpersonal functioning, and social problem-solving abilities all rely on children’s early verbal and EF capabilities. EF and language are similar in the sense that they are both multidimensional constructs that comprise of effortful and interrelated components. Although developmental research illustrates that EF is best represented as a unitary construct in early childhood (Wiebe et al., 2011), language can be divided into three domains (i.e., form, content, and use) that converge in the successful comprehension and production of communicative messages (Bloom & Lahey, 1978). Vocabulary development falls within the language content domain, and it is of particular interest to developmental researchers. This is because not only does vocabulary acquisition begin in infancy and extend across early childhood, but it appears to play a role in understanding and completing goal-oriented cognitive tasks (Fenson et al., 1994; Vygotsky, 1978). Likewise, EF has its roots in infancy and may enable children to focus on linguistic input in the pursuit of early vocabulary building (Blankson et al., 2011).

It is not surprising then that a wealth of literature has reported an association between EF and vocabulary in early childhood (e.g., Carlson et al., 2004; Carlson et al., 2005; Fuhs & Day, 2011; Kuhn et al., 2014; Weiland et al., 2014). For instance, Kuhn et al. (2014) report that communicative gestures in infancy were indirectly related to children’s EF in preschool through toddler expressive vocabulary. The association between EF and vocabulary extends not only across demographically diverse samples but also across both typically and atypically developing child populations (Figueras et al., 2008; Harvey & Miller, 2017). Even among studies that only examine vocabulary as a covariate or proxy variable, significant relations between EF and vocabulary emerge (Cuevas & Bell, 2014; Kraybill et al., 2019; McAlister & Peterson, 2006). Given these robust findings, it follows that these two processes may co-develop and even influence one another in early childhood.

That said, contradictory findings regarding the nature of the association between vocabulary and EF have been documented, especially within the longitudinal literature. As an example, Schmitt et al. (2019) report significant bidirectional links between preschoolers’ EF and verbal abilities in the fall and spring of the academic year. That is, preschoolers’ EF scores in the fall predicted their spring vocabulary size, and children’s vocabulary size in the fall predicted their EF outcomes in the spring of preschool. In contrast, although Gooch et al. (2016) measured the same constructs at similar ages, the cross-lagged effects from EF to vocabulary and vocabulary to EF were not significant. These findings illustrate that the predictive link between childhood vocabulary and EF is inconsistent even among studies with comparable experimental designs. Of course, interpreting analytic findings across studies is made all the more challenging when considering the diverse methodologies adopted by researchers and their divergent operationalizations of key constructs. For example, although both Schmitt et al. (2019) and Gooch et al. (2016) utilized a battery of EF tasks that they then combined, there was little overlap in the individual tasks these authors administered. Even though this is not an uncommon practice considering the array of EF tasks available to early childhood researchers, it is possible that some of the disagreement reported in the literature may be attributable to differences in task selection and resulting composite variables.

Because both vocabulary and EF are critical to a host of child outcomes, understanding the developmental progression of these seemingly interrelated processes is essential to establishing effective and efficient early childhood interventions. A close inspection of the literature is therefore warranted to clarify the nature of the association between EF and vocabulary development and to highlight factors that may be contributing to variability in the research findings across studies. A scoping review was used to synthesize the evidence regarding the longitudinal link between EF and vocabulary in early childhood as well as to determine the volume of research and the way the research was conducted. A scoping review is the recommended review format when attempting to provide an overview of the empirical evidence and to identify gaps in the research when a body of literature has not yet been extensively reviewed (Munn et al., 2018; Peters et al., 2015). To the best of our knowledge, no published articles have reviewed the quantitative research examining the association (longitudinal or otherwise) between EF and vocabulary from late infancy through the kindergarten years. Thus, a scoping review was conducted as it was deemed most appropriate given the state of the early childhood literature as well as the aims of the present review. After providing some background on the individual developmental trajectories of EF and vocabulary below, our scoping review focused on three primary review objectives which were guided by the following research questions:

1. Laying the groundwork: What hypothetical causal models exist in the early childhood literature that can account for the relation between EF and vocabulary?

2. Reviewing the empirical literature: What developmental trends emerge regarding the association between EF and vocabulary when examining the longitudinal research?

3. Identifying gaps in the research: What are some pertinent sources of variability that exist across research paradigms in this domain that may be contributing to disparate findings and relatedly, future directions that may serve to advance this area of study?

Vocabulary acquisition is inherently socially communicative, meaning that the ability to comprehend (i.e., receptive) and eventually produce (i.e., expressive) words is dependent upon early exposure to speech from a mature linguistic partner. Even very young infants are sensitive to and captivated by the linguistic information present in their environment, despite their inability to derive its meaning (Cooper & Aslin, 1990). For example, infants under 6- to 8-months of age can detect auditory consonant-vowel speech contrasts in both their native and non-native languages (Werker & Tees, 2002). Werker and Tees (2002) show that monolingual, English-learning 6-month-olds are capable of perceiving both the English /ba/-/da/ contrast and the [novel] Hindi /ṭa/-/ta/ contrast. Superior phonetic perception in early infancy is predictive of vocabulary outcomes in toddlerhood (Tsao et al., 2004), and infants experience a marked decline in their ability to detect non-native phonemic contrasts toward the end of their first year (Kuhl et al., 2006; Werker & Tees, 2002). This early preference for and sensitivity to speech is therefore vital to cueing infants into the phonetic properties of novel words that they will eventually recognize and even produce.

Across the first postnatal year, infants also commonly engage in prelinguistic communication as a precursor to word production (see Fig. 1; Morgan & Wren, 2018). Very young infants often produce “protophones” (i.e., speech-like vocalizations such as high-pitched squeals or vowel sounds) and make the transition to babbling starting around 6-months of age (i.e., producing fully formed consonant-vowel syllables such as “dada” or “baba”; Lee et al., 2018). Interestingly, Choi et al. (2019) report that obstructing preverbal infants’ oral-motor movements interferes with their discrimination of select auditory speech contrasts. Thus, prelinguistic communication in infancy appears to influence early speech perception as well as precede later speech production.

Vocabulary development is heavily influenced by repeated exposure to words across a variety of contexts, such as during parent-child booking reading (Hart & Risley 1995; Horst, 2013). Researchers report differences in the emergence of receptive and expressive language despite being strongly correlated throughout early childhood. Most children begin comprehending words by 9-months of age but do not produce their first recognizable words until the end of their first year (Fenson et al., 1994). Children’s first spoken words tend to be nouns (and they are commonly names for people), although there is evidence that the strength of this early “noun bias” may vary as a function of cultural context as well as study methodology (Alcock, 2017). In contrast, children’s early receptive vocabularies tend to include a comparatively larger proportion of verbs (Bates, 1979). From there, vocabulary growth is slow during the first half of children’s second year yet increases rapidly starting around 18 months and continuing through the preschool/kindergarten years (Fenson et al., 1994). In part, this trend may reflect 2-year-olds’ drastically improved ability to utilize social information (e.g., eye gaze) in discerning ambiguous word-referent pairings in comparison to infants (Golinkoff & Hirsh-Pasek, 2006). This rapid vocabulary expansion in toddlerhood enables children to begin using language in an increasingly complex manner. For instance, despite the unique and complicated way in which pronouns can be used as substitutes for nouns, preschoolers demonstrate a strong understanding of how first- and second-person pronouns operate (Campbell et al., 2000). Taken together, steady progression in speech perception in early infancy gives way for the extensive vocabulary growth that originates near the end of the first postnatal year and extends across the early childhood period.

Finally, although the linguistic focus of our scoping review is on spoken receptive and expressive vocabulary, there are aspects of language acquisition that also progress during early childhood which are not presently discussed. In part, our focus on vocabulary is reflective of the available literature’s general emphasis on vocabulary development which, as discussed above, may stem from the early emerging course of vocabulary acquisition that extends across much of the early childhood period. There are also notable methodological constraints to examining other facets of language. In contrast to pre-linguistic communication or narrative ability, for example, there are many rigorously evaluated and industry-standard measures of vocabulary comprehension and/or production available to developmental researchers (e.g., the Peabody Picture Vocabulary Test). Lastly, some factors, such as narrative skill, may reflect not only children’s language capabilities but also their socioemotional and theory of mind skills (Gamannossi & Pinto, 2014; Peterson & Biggs, 2001). In focusing on vocabulary development then we are able to limit the potential overlap between language and other socio-cognitive aspects of development.

Although there is a lack of agreement on a formal definition, EFs are generally understood to be effortful, top-down cognitive processes that enable individuals to engage in goal-directed behaviors such as planning, problem-solving, and monitoring/adjusting one’s behavior (Diamond, 2013). Significant maturational changes to the prefrontal cortex are foundational to the emergence of EF in late infancy and promote improvements in EF across early childhood (Diamond, 2002; Fiske & Holmboe, 2019). The toddler and preschool years are of particular interest to researchers because they mark the transition from infancy where children are beginning to be expected to modulate their behavior, often in contexts outside the home. For example, in an early childhood classroom, young children rely heavily on EFs to successfully perform everyday tasks such as raising their hand and waiting to be called on, transitioning from free-play to structured activities, and following a list of instructions to “pack up your things, push in your chair, and line up by the door.” As such, EF abilities develop rapidly across the first few years and are directly related to academic performance and self-regulatory behavior (Blair & Razza, 2007; Diamond, 2013).

EFs are typically thought to be comprised of three core components: Inhibitory control (the ability to exert control over one’s attention/thoughts/behaviors to do what is contextually appropriate or necessary), working memory/updating (the ability to hold information in the mind and manipulate it), and cognitive flexibility/shifting (the ability to switch between tasks/mental states and adjust to changing demands; Diamond, 2013). There has been a longstanding debate about how EF is operationalized and measured in childhood. Of particular interest to researchers is whether EF represents a unitary construct or a constellation of independent components, as well as the degree to which the factor structure of EF is stable across development. Research with adults using confirmatory factor analysis has identified a three-factor model comprised of inhibition, updating, and shifting (Miyake & Friedman, 2012; Miyake et al., 2000). In this sense, these factors represent distinct yet interrelated components that may be differentially employed based on a particular task. This factor structure has been replicated in research with older children ages 8–13 (Lehto et al., 2003). The early childhood literature, however, points to a more integrative framework for studying EF. That is, a two-factor model (working memory and inhibitory control) has been proposed for children starting around 5 years of age (Roberts & Pennington, 1996; Carlson, 2005), while the best-fitting model for children around 3 years of age is a one-factor model (Wiebe et al., 2011).

Developmental differences in the factor structure of EF may be due to the fact that early childhood EF appears to build upon rudimentary skills in infancy (i.e., attention or information processing; Blankenship et al., 2019). Additionally, more complex EF tasks are thought to tap into non-EF domains such as motor or linguistic abilities (Fuhs & Day, 2011). For example, McClelland et al. (2014)'s Head-Toes-Knees-Shoulders task requires children to locate and touch different areas of the body (gross motor ability) based on their understanding of the experimenter’s instructions (verbal ability). As such, EF tasks may differentially “hang together” depending upon their shared reliance on children’s non-EF skills. Finally, many early childhood EF tasks are thought to assess multiple cognitive components, a frequently addressed issue known as task impurity (Fuhs & Day, 2011). Finding evidence for a two-factor model in preschool children, Miller et al. (2012) argue that the factor structure of EF in childhood may be influenced in part by task selection. However, given the wealth of research supporting the one-factor model in early childhood (Garon et al., 2008), we will largely focus on the link between vocabulary development and EF as a unitary construct.

EFs emerge in infancy and develop swiftly across childhood (Fatzer & Roebers, 2012; Garon et al., 2008). Although not a primary focus here, the orienting network of attention appears to lay the groundwork for the development of cognitive self-regulatory abilities in childhood (see Fig. 1; Blankenship et al., 2019). In this sense, the orienting network (which is responsible for one’s ability to engage, disengage, and shift attention) is thought to facilitate EF-related skills such as suppressing one’s attention to a distracting stimulus (inhibitory control) or keeping one’s attention focused on information being held in the mind (working memory; Diamond, 2013; Johnson, 1990). Indeed, research has found that infant attention predicts EF skills across early and middle childhood (Cuevas & Bell, 2014; Garon et al., 2008; Kraybill et al., 2019).

Because there are a limited number of infant EF tasks available to researchers, much of the literature to date has focused on the A-not-B task (Bell, 2012; Diamond et al., 1997). This task is one of many multilocation search tasks where infants must inhibit the urge to search for an object in a familiar location (location A) having observed that the object was hidden in a new location (location B). A-not-B task performance improves with age, such that longer delays between hiding and searching are needed to produce the error with older infants. In this sense, young infants’ preservative responses (i.e., searching at location A after seeing the toy hidden a location B) may be due to immature inhibitory control skills early in life. However, it may be that older infants’ errors on trials with larger delays are indicative of the A-not-B task’s working memory demands (Cuevas & Bell, 2014; Wiebe et al., 2010).

In contrast to infants, toddlers and preschoolers exhibit more advanced motor and linguistic skills, which means that there are a greater number of tasks appropriate for assessing EF in this age range. As indicated above, inhibitory control emerges early in life but is disproportionately difficult for young children (Diamond, 2013). In the toddler/preschool years, dramatic improvements in inhibitory control have been reported across delay-of-gratification and conflict inhibition tasks, and early inhibitory control abilities are predictive of developmental outcomes extending into adulthood (Carlson, 2005; Diamond, 2013; Joyce et al., 2016). Working memory abilities also appear early in development and by toddlerhood, most children can complete working memory tasks such the spinning and stationary pots (Diamond et al., 1997; Miller & Marcovitch, 2015; Wiebe et al., 2010). Nonetheless, the ability to simultaneously hold multiple items in the mind and complete complex mental operations develops much slower. Although EF tasks are often labeled as being either an inhibitory control or working memory task, Diamond (2013) argues that these cognitive processes are closely related and frequently operate in tandem. For instance, to inhibit a behavior, an individual must hold a goal or set of instructions in the mind; to hold/manipulate information in the mind, an individual must inhibit the urge to shift their focus elsewhere. It is not surprising then that cognitive flexibility, which is thought to build upon children’s working memory and inhibitory control skills, emerges relatively later in early childhood (Blakey et al., 2016; Diamond et al., 2005). On the Dimensional Change Card Sort Task (DCCS), toddlers experience significant difficulty in switching between sets of conflicting instructions. However, by the time children reach the kindergarten years, most can successfully switch between sorting dimensions on the DCCS (Diamond, 2013).

As a foundation for examining the hypothetical causal models that can account for the association between EF and vocabulary (question 1 of this scoping review), we addressed the independent developmental courses of EF and language. However, both clinical and developmental researchers have demonstrated that deficits in one domain (i.e., EF or vocabulary) influence performance in the other. For instance, Henry et al. (2012) report that children diagnosed with selective language impairment exhibited poorer performance on a series of EF tasks in comparison to children without language impairment, even after controlling for age and IQ. Among typically developing (TD) child samples, performance on complex working memory tasks worsens when children are asked to simultaneously complete a verbal (but not motor) task (Fatzer & Roebers, 2012). Thus, it appears that EF and vocabulary are closely related in childhood.

Coming from a clinical neuropsychology perspective, Bishop and colleagues (2014) present a useful framework for thinking about the observed link between deficits in EF and language impairment. Their theoretical framework illustrates three possible causal models depicting the association between EF and language more broadly: (model A) EF abilities impact language; (model B) language skills impact EF; (model C) a third factor independently influences EF and language development (see Fig. 2). Bishop et al. (2014) argue that models A and B may operate at either the superficial level (e.g., a “language task” requires EF skills) or the deep level (e.g., EFs are inherently involved in producing words). What is missing from Bishop et al.’s models, however, is the temporal precedence required to better evaluate whether a causal link exists between EF and verbal skill across childhood. As such, we extend Bishop et al.’s original framework in the present review by applying a developmental approach to models A–C and by presenting a novel, fourth model (model D) that addresses the potential for a bidirectional association between EF and verbal ability in early childhood (see Figure 2). What follows is a comprehensive discussion of these four models from a longitudinal perspective, which includes select yet relevant research that supports each hypothetical developmental pathway between EF and vocabulary specifically.

This first model postulates that EF skills are predictive of vocabulary outcomes in early childhood. In comparison to model B (vocabulary predicts EF), relatively fewer clear rationales regarding this developmental pathway have been presented in the literature. One possible explanation for this difference is that much of the longitudinal research has examined the degree to which EF predicts an array of academic outcomes (e.g., math, literacy, and verbal ability) as opposed to just vocabulary (e.g., Cameron et al., 2012; McClelland et al., 2007; McClelland et al., 2014; Ponitz et al., 2009). As such, these studies frequently provide a rationale for the association between EF and academic achievement as a whole instead of addressing each academic subdomain.

Nonetheless, Blankson et al. (2011) suggest that EF, and in particular, inhibitory control, may enable children to direct their attention to linguistically relevant information in the environment and inhibit shifting to salient yet irrelevant distracting events. These authors report a significant interaction between EF and environmental stimuli in the prediction of preschool vocabulary. Therefore, it may be the case that when provided sufficient environmental stimulation (e.g., children’s access to books and someone to read to them), children’s early EF abilities facilitate word learning. Alternatively, Netelenbos et al. (2018) argue that to effectively communicate with a social partner, children rely on working memory to bring to mind a particular concept and hold it there as they simultaneously assemble and produce the intended message. In line with this interpretation, Gathercole and Baddeley (1989) show that preschoolers’ phonological working memory skills on a non-word repetition task were predictive of their vocabulary outcomes a year later, even after accounting for initial verbal scores. As such, it is reasonable to theorize that various aspects of children’s emerging EFs may give rise to vocabulary development in childhood.

In contrast to model A, this model asserts that vocabulary size is causally related to the advancement of EF. Indeed, having a sufficiently large vocabulary may be essential to the successful execution of goal-oriented activities such as holding a set of rules in the mind to translate thought into action. At a basic level, it could be argued that in order to complete an EF task a child must first be able to comprehend that task’s instructions. We will revisit this idea in greater detail in our discussion (see “Potential Sources of Variability in the Findings Across the Longitudinal Literature”). According to Vygotsky (1978), however, private speech (i.e., overt speech directed to the self) is central to the development of self-control via higher-order cognitive operations in childhood. In other words, children rely on culturally bound symbols (e.g., words) in the service of manipulating and self-directing thought/action, which becomes internalized over the course of development. Winsler et al. (1997) report that when presented with a difficult cognitive task, the majority of preschoolers emitted some form of private speech, where greater task-relevant private speech was associated with superior task performance. As such, early word learning may be an important precursor to the development of EF in childhood.

Beyond serving as a catalyst for cognitive self-regulatory behavior, one’s vocabulary size may also influence their ability to mentally represent a problem and develop a plan of action. According to the Cognitive Complexity and Control Theory (CCCT; Zelazo et al., 2003; Zelazo, 2006), speech enables children to evaluate relations between hierarchical and competing sets of rules to respond appropriately and flexibly in a given context. For example, to correctly sort cards presented during the Dimensional Change Card Sort task (DCCS), children must first comprehend the words that stipulate the incompatibility of the pre- and post-switch rules before determining which set of rules to apply (i.e., “When playing the ‘color game,’ the red cards go in location A and the blue cards go in location B, regardless of shape. When playing the ‘shape game,’ the rabbit cards go in location A and the boat cards go in location B, regardless of color”). Indeed, Karbach and Kray (2007) report age-related differences in the content of children’s self-verbalizations when “thinking out loud” on a switching task. These authors found that while 5-year-olds frequently verbalized the target (i.e., they named the object they saw), 9-year-olds consistently verbalized the instructional cue and response (i.e., they named the sorting rule and required action) and exhibited a significantly lower error rate in comparison to the younger group. Thus, CCCT maintains that vocabulary development supports children’s ability to represent a problem, categorize an embedded set of verbal rules, and respond accordingly when presented with complex EF tasks.

Model C asserts that EF and vocabulary are not causally related; rather, these processes tend to co-occur because they are mutually influenced by an independent third factor. Bishop et al. (2014) specifically propose that damage to or delays in the maturation of the frontal lobes may negatively impact brain areas linked to the development of both EF and language in general. To date, a wealth of research has indicated that frontal lobe functioning is associated with speech and syntactic processing, vocabulary comprehension/production, and EF (Braakman et al., 2011; Fiske & Holmboe, 2019; Moriguchi & Hiraki, 2013), thereby illustrating that structural and functional differences in the brain may result in atypical cognitive-linguistic development in childhood. There is also data to suggest that early emerging, child-centric abilities such as infant attention or motor development may serve as developmental precursors to the onset of vocabulary acquisition and EF (Blankenship et al., 2019; Kent, 1984; Salley et al., 2013). Lastly, given the social origins of cognitive-linguistic development, it is also possible that contextual factors present early in development, such as caregiving behaviors, may promote or impede child EF and word learning (Baumwell et al., 1997; Bernier et al., 2010).

Of course, these are just a select few examples of potential tertiary factors based on the developmental literature. From an ecological systems perspective, various factors at the level of the child (genetics, brain maturation, temperament, etc.) and their environment (parenting, early childhood education, socioeconomic status, etc.) may separately and/or collectively shape the development of EF and vocabulary. Given the overwhelming abundance and diversity of research examining various biopsychosocial factors that independently impact both EF and vocabulary development, a thorough examination of the literature exploring model C is beyond the scope of this review. That is, to do justice to the investigation of model C, an independent review of the early childhood literature is undoubtedly required. Nonetheless, the notion that individual differences and/or environmental factors may contribute to the development of EF and vocabulary will be discussed below in greater detail as both a limitation of the present scoping review and future research direction.

Finally, one drawback to the causal models presented by Bishop et al. (2014) is the absence of a bidirectional model, given that the relations depicted in models A and B are not mutually exclusive. For example, using a causal chain analytic approach, a researcher may find that early word knowledge in infancy exerts a direct influence on EF in toddlerhood (model A), which in turn directly impacts preschool vocabulary outcomes (model B). Alternatively, using a cross-lagged panel design, a researcher could report that children’s vocabulary size in toddlerhood predicts their EF abilities during the preschool years (model B) and that children’s EF skill in toddlerhood is predictive of their vocabulary size as preschoolers (model A). We can therefore envision a fourth model (model D) which represents a possible recursive pathway between EF and vocabulary development across early childhood.

Having discussed multiple hypothetical causal models in the paragraphs above, the following section encompasses our in-depth scoping review of the longitudinal literature regarding the association between EF and vocabulary in early childhood (question 2). Specifically, we evaluated whether any developmental trends emerged in the literature and to what extent the presented causal models were or were not supported by the longitudinal research. Thus, to better capture the nature of the predictive link between EF and vocabulary, we included studies exploring both unidirectional (models A and B) and bidirectional (model D) relations between EF and vocabulary.

A scoping review of the literature was conducted to identify and map the available evidence regarding the developmental association between EF and vocabulary. To minimize the potential for selection bias in the literature extraction phase, the authors employed a standardized data extraction tool and adhered to the best practice guidelines presented by both Ferrari (2015) and Peters et al. (2015) for organizing and writing an empirically informed, non-systematic review paper.

Articles were included in the review if they met the following criteria: (a) the assessment of both EF and vocabulary were a primary focus, (b) the data were longitudinal (i.e., there were at least two waves of data collection), (c) the age range of the sample fell between approximately 12-months to 5-years, and (d) the research was empirical and published in a peer-reviewed journal. The lower age limit was set at 12-months as both EF (Diamond, 2013) and vocabulary (Fenson et al., 1994) emerge toward the end of children’s first postnatal year. Because individual differences in EF solidify across early childhood and are predictive of later academic functioning and mental health (Helm et al., 2019; Morgan et al., 2019), the upper age and/or grade level limit was set at age 5/kindergarten-aged. Articles were excluded from the review if the selection criteria were not met or if the study was conducted with a sample of children that (a) were bilingual, (b) had been diagnosed with a neurodevelopmental disorder (e.g., autism spectrum disorder), (c) were hearing impaired, (d) had a history of brain injury, or (e) were born preterm. The article search was conducted from March 22nd through March 26th, 2021, across two electronic databases: PsycINFO and PubMed. Given the developmental focus of our scoping review, we selected two subject-specific databases, one that is freely available and one that is widely used in the discipline, that yield published and peer-reviewed literature. The search terms used in different combinations were “Executive Function,” “Executive Functioning,” “Executive Control,” “Language,” “Vocab*,” “Word Learning,” “Lexical Development,” “Childhood (birth – 12),” “Toddler*,” “Preschool*,” “Kindergarten*.” The reference sections of all included articles were additionally searched for any missing publications.

In total, 23 articles were eligible for inclusion in the present review (see Table 1 for a brief overview of the study characteristics and primary findings). Included studies were predominantly conducted in the United States (n = 17; 74%); however, 3 studies were completed in Canada (Matte-Gagné & Bernier, 2011; Müller et al., 2012; Wade et al., 2014), 2 studies were completed in the United Kingdom (Gooch et al., 2016; Hughes & Ensor, 2007), and one study was completed in China (Chung & McBride-Chang, 2011). Sample sizes ranged from 47 to 1,121 children, and most studies (n = 19; 83%) recruited an equal number of boys and girls in their sample (i.e., 50% girls ± 5%). Across the articles included in this review, there was some diversity in the sample demographics. In 9 of the 23 studies (39%), a majority of the participants identified with a race or ethnic group other than White/Caucasian (i.e., Hispanic, African American/Black, Asian, or multiracial/other). In 10 of the 23 studies (43%), a low socioeconomic status (SES) sample was recruited, which was determined based on available reports of familial income, education attainment, geographical location, and/or use of federal assistance programs.

Of the included articles, 6 studies (26%) measured only receptive vocabulary, 5 studies (22%) measured only expressive vocabulary, and 12 studies (52%) measured both receptive and expressive vocabulary. Child vocabulary was commonly measured using a standardized behavioral assessment (n= 21; 91% of all included studies), although vocabulary was also evaluated via parent report (n = 4; 17% of all included studies) or behavioral observations during a parent-child activity (n = 1). The most frequently administered vocabulary assessments were the Picture Vocabulary and/or Oral Comprehension subtests on the Woodcock-Johnson III Tests of Achievement (WJ-III; n = 8, 35% of all included studies; Woodcock et al., 2001) and the Peabody Picture Vocabulary Test (PPVT; n = 7, 30% of all included studies; Dunn & Dunn, 2007). To assess child EF, most of the studies employed a battery of behavioral EF tasks (ranging from 2 to 10 tasks administered in total with a median number of 5 tasks). Only 4 studies (18%) used a single indicator (i.e., the Dimensional Change Card Sort task (DCCS; Zelazo et al., 1996) or the Head-Toes-Knees-Shoulders task (HTKS; McClelland et al., 2007)) as the EF metric. Across all of the included articles, 40 different EF tasks were employed. The most frequently administered tasks across all included studies were HTKS (n = 9; 39%), DCCS (n = 7; 30%), Day/Night (n = 6; 26%; Gerstadt et al., 1994), Animal Go/No-Go (n = 5; 22%; Durston et al., 2002), and some version of Bear/Dragon (n = 5; 22%; Reed et al., 1984).

Finally, of the 23 studies included in this review, 8 studies (35%) evaluated bidirectional relations between EF and vocabulary development. Among the remaining studies that investigated unidirectional pathways, 9 studies (39%) examined whether early vocabulary size predicted later EF, and 6 studies (26%) assessed whether early EF predicted later vocabulary outcomes. The findings from the literature summarized below are therefore organized in sections based on the authors’ examination of the association between EF and vocabulary in keeping with our longitudinal adaptation of Bishop et al. (2014)'s unidirectional models as well as our addition of the bidirectional model.

Among the studies that exclusively examined whether EF impacts vocabulary development, all 6 reported significant, positive correlations between children’s EF and vocabulary scores. However, after controlling for children’s initial vocabulary size, only 3 studies (50%) reported that early EF predicted later vocabulary outcomes (Fuhs et al., 2015; McClelland et al., 2014; Willoughby et al., 2017). Through a series of multilevel models, Fuhs et al. (2015) illustrated that preschoolers’ fall EF scores were predictive of their vocabulary outcomes in the spring after entering children’s pretest vocabulary scores as a covariate. Fuhs and colleagues noted that teacher reports of child EF accounted for more variance in preschool vocabulary gains in comparison to the direct EF assessments. Similarly, McClelland et al. (2014) reported that children’s EF abilities at the start of the school year were predictive of their vocabulary size at the end of the year across both preschool and kindergarten, even after controlling for their vocabulary scores in the fall. Finally, Willoughby et al. (2017) demonstrated that EF growth from age 3 to 5 was related to children’s vocabulary outcomes at age 5 after controlling for children’s initial vocabulary scores.

The remaining 3 studies did not reveal a significant direct effect of EF on vocabulary after controlling for children’s initial verbal scores (Cameron et al., 2012; McClelland et al., 2007; Ponitz et al., 2009). Of note, all 3 of these studies that reported an insignificant association used a single indicator (i.e., scores on the HTKS task) as the measure of child EF. It is therefore reasonable to propose that these null findings may speak to the relation between vocabulary acquisition and this particular task as opposed to EF as a multidimensional construct. Finally, all 6 of the studies discussed here only measured EF and vocabulary when children were 3 years of age or older, and 4 out of the 6 studies (67%) only collected two waves of longitudinal data (Cameron et al., 2012; Fuhs et al., 2015; McClelland et al., 2007; Ponitz et al., 2009). In sum, these studies consistently reported that children’s early EF scores were positively correlated with their later vocabulary scores. However, there was moderate evidence to suggest that EF at the start of preschool/kindergarten is predictive of children’s vocabulary outcomes later in preschool/kindergarten when controlling for children’s starting vocabulary level. Based solely on these studies, it remains unclear whether early EF significantly and uniquely predicts vocabulary development, especially prior to the preschool years.

Similar to the previous section, all 9 articles that tested a unidirectional relationship between early vocabulary and later EF found these factors to be significantly, positively correlated. After controlling for children’s baseline EF scores, 5 studies (56%) reported that early vocabulary scores were significantly predictive of children’s subsequent EF outcomes (Hughes & Ensor, 2007; Kuhn et al., 2016; Matte-Gagné & Bernier, 2011; Miller & Marcovitch, 2015; Müller et al., 2012). Matte-Gagné & Bernier (2011) illustrated that 2-year-olds’ expressive vocabulary was predictive of their age 3 EF skills. Additionally, these authors found that vocabulary mediated the relationship between maternal parenting at 15-months and EF performance at age 3. Likewise, Müller and colleagues (2012) showed that children’s receptive vocabulary at age 3 was predictive of their EF at age 4, and that vocabulary size mediated the relationship between children’s theory of mind skills at age 2 and their EF outcomes at age 4. Together, these studies not only highlight a direct effect of child vocabulary on EF, but they also suggest that early word knowledge/production may underlie the relationship between contextual or child-centric factors during the second year and later EF.

Next, although Kuhn et al. (2016) found that age 3 vocabulary was not significantly associated with age 5 EF, these authors reported that changes in children’s expressive vocabulary from 15- to 36-months were predictive of both children’s EF growth from 36- to 60-months and their age 5 EF scores. That is, individual differences in children’s rate of early vocabulary acquisition were related to their EF scores at age 5 and EF growth across early childhood. After controlling for social disadvantage as well as children’s theory of mind and initial EF scores, Hughes and Ensor (2007) reported that vocabulary scores were a significant predictor of EF a year later. In this sense, age 2 receptive and expressive vocabulary was predictive of age 3 EF, and age 3 vocabulary was predictive of age 4 EF. Although children’s EF abilities at ages 2 and 3 were correlated with their vocabulary scores at ages 3 and 4, the authors did not explicitly evaluate the inverse developmental pathway (i.e., whether children’s early EF scores predicted their vocabulary level a year later). Finally, Miller and Marcovitch (2015) found that receptive vocabulary size at 14-months was predictive of the number of EF tasks children passed at 18-months, thereby highlighting the importance of infant vocabulary for EF in early toddlerhood. Interestingly, these authors reported that the relationship between 14-month expressive vocabulary size and 18-month EF was not significant. However, this difference between expressive and receptive vocabulary may have been due to limited variability in children’s reported word production scores at 14-months.

Of the remaining 4 studies, one reported that 24-month expressive vocabulary was not a significant predictor of EF at 39-months after controlling for children’s starting EF scores (Carlson et al., 2004) and 3 did not include children’s initial EF scores as a covariate (Daneri et al., 2019; Wade et al., 2014; Whedon et al., 2018). Nonetheless, Daneri et al. (2019), Wade et al. (2014), and Whedon et al. (2018) all reported that 36-month receptive vocabulary was predictive of either 48-month or 54-month EF. Whedon and colleagues (2018) additionally reported that 24-month expressive vocabulary was related to 48-month EF. Given the significant relations that emerged across multiple developmental timepoints, together these studies suggest that early word learning plays a role in predicting children’s later EF outcomes.

The remaining 8 studies evaluated whether a bidirectional relationship exists between EF and vocabulary size. Of these studies, only one reported that the measures of EF and vocabulary were not significantly correlated (concurrently or longitudinally; Chung & McBride-Chang, 2011). Three out of 8 studies (38%) found evidence supporting the hypothesized bidirectional association between EF and vocabulary (Fuhs et al., 2014; Kuhn et al., 2014; Schmitt et al., 2019). After controlling for children’s initial scores, Fuhs et al. (2014) reported that (a) children’s word comprehension skills at the start of preschool were predictive of their EF skills at the end of preschool and (b) preschoolers’ EF abilities at the start of the year were predictive of their receptive vocabulary scores assessed at the end of the year. Additionally, children’s EF skills at the end of preschool were related to their vocabulary comprehension scores at the end of kindergarten; however, the inverse pathway was not significant in the authors’ model. Similarly, Schmitt et al. (2019) indicated that receptive vocabulary at preschool entry was predictive of children’s EF scores at the end of preschool when controlling for entry EF skill. These authors also reported that fall EF significantly predicted vocabulary in the spring of preschool, thereby illustrating a bidirectional relationship between these processes across the preschool year. Lastly, Kuhn et al. (2014) reported that both 24- and 36-month expressive vocabulary exerted a significant direct effect on 48-month EF after controlling for familial socioeconomic status, maternal parenting, and 24-month EF. Additionally, these authors discovered an indirect effect of 24-month EF on 48-month EF through 36-month expressive vocabulary.

Comparatively, 3 different studies (38%) reported evidence supporting only a unidirectional pathway between EF and vocabulary. That is, Weiland et al. (2014)'s finding supports model A (EF → vocabulary), whereas both Fuhs & Day (2011) and Petersen et al. (2015) findings support model B (vocabulary → EF). Having also examined relations across the preschool year, Fuhs and Day (2011) reported that children’s starting expressive/receptive vocabulary skills were predictive of their EF abilities at the end of the school year, with children’s starting EF scores entered as a covariate. The inverse pathway was not significant after controlling for children’s starting vocabulary size. Petersen et al. (2015) reported similar findings in that children’s vocabulary size at ages 2.5 and 3 were predictive of their EF skills at ages 3 and 3.5, respectively, after controlling for their initial EF scores. There was no association, however, between early EF and later vocabulary outcomes. In contrast, Weiland et al. (2014) revealed that only preschoolers’ EF skills at the start of the school year were significantly related to their receptive vocabulary outcomes at the end of the school year after controlling for children’s starting vocabulary size.

Finally, the 2 remaining studies reported that neither EF nor vocabulary were predictive of children’s later cognitive/linguistic outcomes (Chung & McBride-Chang, 2011; Gooch et al., 2016). Specifically, Chung & McBride-Chang (2011) and Gooch et al. (2016) found no evidence that EF and vocabulary were longitudinally predictive of one another across the preschool and kindergarten years. Gooch and colleagues (2016) reason that significant cross-lagged effects may not have been detected in their study as their results show a considerable degree of stability in children’s vocabulary and EF scores over time.

When considering all 23 studies included in the current review, it is evident that vocabulary and EF are indeed correlated both concurrently and longitudinally in early childhood. However, some of the studies in this review did not measure both EF and vocabulary at each developmental time point and as a result, these studies could not partial out children’s initial EF/vocabulary scores. This makes it difficult to evaluate, for example, whether early word learning accounts for unique variance in children’s later EF outcomes, above and beyond what would be accounted for by their more rudimentary EF skills. Additionally, all 10 studies that recruited a low socioeconomic status sample reported significant longitudinal relations between EF and vocabulary. Although not of primary interest here, this unexpected difference as a function of socioeconomic status suggests that environmental factors such as familial income or parental education should be taken into consideration as they may influence the predictive association between EF and vocabulary in early childhood.

Collapsing across studies examining uni- and bidirectional pathways, 14 studies analyzed whether earlier EF is related to vocabulary size later in childhood. Of these, only 7 studies (50%) found evidence to support this predictive association (i.e., model A). Regarding the inverse pathway, 13 out of 17 studies (76%) reported that earlier child vocabulary predicted later EF abilities (i.e., model B). Thus, a greater number of studies overall found evidence that early vocabulary size predicts children’s EF outcomes. Finally, 3 out of 8 studies (38%) reported significant bidirectional links between vocabulary and EF (i.e., model D). There was some disagreement in the results reported across studies, and there were notable differences in the study designs utilized by researchers, which together made it challenging to delineate clear developmental trends in the literature. Thus, we turn to our third question regarding the existing gaps in the developmental literature by identifying key factors that may be contributing to some of the disagreement across studies and select avenues for future research.

In infancy, there are a limited number of EF tasks available to researchers. However, significant improvements in children’s linguistic and motor abilities across the second year give way for a greater assortment of developmentally appropriate EF tasks (see Garon et al., 2008 for a comprehensive discussion about early childhood EF tasks). One factor that may be contributing to mixed findings regarding the longitudinal relationship between EF and vocabulary is the lack of consistency concerning how EF is measured in early childhood. As previously stated, a total of 40 different EF tasks were administered among the 23 studies included in this review. Thus, some of the reported disagreement may be due to differences in task selection across studies. For example, Fuhs and Day (2011), Schmitt et al. (2019), and Weiland et al. (2014) all assessed children’s EF and language abilities at the start and end of preschool among samples with similar demographic backgrounds. Yet, these authors reported very different findings. Although Schmitt et al. (2019) demonstrated a bidirectional association between children’s EF/vocabulary scores in the fall and their respective spring outcomes, Weiland et al. (2014) and Fuhs and Day (2011) only reported a unidirectional pathway between EF and vocabulary. Additionally, Weiland et al. (2014) showed that preschoolers’ EF scores in the fall were predictive of their vocabulary outcomes in the spring, yet Fuhs and Day (2011) analyses supported only the inverse pathway in their sample of preschoolers. A crucial difference between these 3 studies, however, was the EF tasks that were administered. Thus, the broad array of EF tasks employed across the studies included in this review makes it difficult to eliminate the possibility that contradictory findings in the literature are simply due to measurement approach differences.

In addition to task selection differences, comparing and integrating collective findings is even more challenging when considering the limited agreement among researchers as to what various EF tasks are actually measuring (Carlson, 2005; Fuhs & Day, 2011). For instance, the Dimensional Change Card Sort (DCCS) task is thought to be a simplified version of the adult Wisconsin Card Sorting Task as the DCCS requires children to similarly sort cards but by fewer dimensions and based on explicit trial instructions (Zelazo, 2006). Although some researchers claim that the DCCS task captures children’s attentional flexibility (which is thought to involve shifting attention between task features; Fuhs et al., 2015), others argue that the DCCS measures task-switching abilities (which is thought to involve shifting between tasks/sets of instructions; Diamond et al., 2002) or even multiple cognitive domains (e.g., attention, working memory, and inhibitory control; Watson & Bell, 2013). Without conceptual and analytic clarity regarding the underlying skills various EF tasks are tapping into in childhood, it is unclear whether tasks are effectively interchangeable and can be selected at random across studies with little to no influence on the results. Additional replication research utilizing latent variable analysis with a clear rationale behind task selection is, therefore, necessary to better evaluate the development of EF and vocabulary in early childhood. When feasible, replication efforts should seek to implement a cross-lagged panel design as this approach allows for the examination of bidirectional causal pathways as a function of time (see Zyphur et al., 2020, for an in-depth account on the appropriate application of cross-lagged panel modeling using human subject data).

Conversely, it is also possible that researchers’ use of various measures of child vocabulary may be contributing to variability in the findings across the longitudinal research (see Xue et al. (2015)'s brief report describing the range of language measures in early childhood); however, this alternative explanation seems less likely. First, no global differences regarding support for models A, B, and D emerged as a function of whether researchers measured expressive vocabulary or receptive vocabulary. For example, collapsing across studies examining uni- and bidirectional pathways, 17 studies evaluated whether vocabulary predicted EF. Among these 17 studies, 10 measured expressive vocabulary (58%) and 13 measured receptive vocabulary (76%; note that these percentages do not add up to 100% because 6 studies measured both expressive and receptive vocabulary). In total, 8 out of the 10 studies measuring expressive vocabulary (80%), and 10 out of the 13 studies measuring receptive vocabulary (77%), found early vocabulary significantly predicted later child EF. Thus, similar developmental trends were identified across studies. Second, all but one study included in our review employed a standardized instrument to assess vocabulary. In contrast to the EF literature, there is little evidence of disagreement or a lack of clarity among early childhood researchers and instrument developers regarding (a) the definition of expressive/receptive vocabulary or (b) what aspects of language development are being measured by standardized assessments. Indeed, one of the benefits of standardized instruments is their ability to provide normative data through which a child’s score can be compared across measures designed to assess the same variable/construct. Many commonly used, standardized language instruments report acceptable and/or high convergent and predictive validity (Bogue et al., 2014; Bridges et al., 2004; Feldman et al., 2005). Thus, it appears that differences in the language assessment administered across studies are unlikely to be significantly contributing to the mixed findings in the literature.

What is clear is that some EF tasks are quite complex and that performance on certain tasks heavily relies on children’s ability to comprehend verbal instructions and/or produce verbal responses (Fuhs & Day, 2011). In returning to the DCCS task as an example, children are typically asked to sort a set of cards first by one dimension (i.e., color), after which children are instructed to switch to a new sorting rule (i.e., shape). In general, 3-year-olds can perfectly sort by either color or shape, but they experience significant difficulty in switching to the new rule (Diamond, 2013; Zelazo, 2006). Performance is greatly improved, however, if children are prompted to verbally state the current rule and label the card’s relevant dimension before sorting each card (Kirkham et al., 2003; Ramscar et al., 2013). Likewise, Schonberg et al. (2018) reported that alterations to the verbal instructions for a reverse categorization task measuring nonverbal cognitive ability significantly influenced 2-year-olds’ task performance. That is, when the experimenters used fewer dimension-related words in their explanation of how to complete the task, toddlers’ performance improved considerably. Even childhood EF tasks that are classified as “nonverbal,” however, are at best minimally verbal as many of these tasks require young children to comprehend some form of verbal instruction. It follows then that the association between vocabulary and EF may be driven in part by this overlap in language demands (Kaushanskaya et al., 2017). Indeed, this would suggest that the extent to which children’s early skills are predictive of their EF/vocabulary outcomes later in childhood may differ across studies as a function of whether researchers administer verbally demanding EF tasks. As such, additional research is needed to explicitly examine the relation between vocabulary and both verbal/nonverbal EF to continue to tease apart this overlap in children’s verbal skills.

Finally, it is also plausible that the predictive association between vocabulary and EF differs between late infancy/toddlerhood and the preschool/kindergarten years. Among the articles included in this review, a greater number reported that children’s vocabulary scores during their second postnatal year were significantly predictive of their later EF outcomes in comparison to the inverse causal pathway. Across the preschool period specifically, however, researchers found that both children’s vocabulary and EF abilities were predictive of their respective scores later in the academic year. Thus, some of the disagreement reported in the literature may be due to genuine differences in the developmental trajectory of these processes as a function of child age, especially since older children are more likely to have acquired the receptive vocabulary necessary to comprehend more complex EF tasks. Of course, the dearth of longitudinal literature examining causal pathways between vocabulary and EF in infancy and even toddlerhood makes this claim largely speculative. Far fewer studies in this review measured children’s EF before the preschool years in comparison to vocabulary. As noted by Gooch et al. (2016), although no evidence of a bidirectional relationship between vocabulary and EF was detected in their study with preschoolers and kindergarteners, this does not rule out the possibility that children’s very early skills may lay the groundwork for those exhibited later in childhood. Furthermore, although longitudinal research allows for the examination of developmental growth and offers the potential to infer causality, many of the studies included in our review adopted a two-wave longitudinal design. This in turn makes it difficult to disentangle true change from measurement error and significantly restricts the assessment of growth over time (Ployhart & MacKenzie, 2015). Taken together, additional longitudinal research starting in late infancy or toddlerhood when EF/vocabulary skills are emerging and rapidly developing is required to clarify whether predictive relations differ as a function of age in early childhood.

Although several publications relate EF to vocabulary development, the originality of this review lies in our focus on the longitudinal nature of the association between these two processes based on the empirical research in late infancy through early childhood. To minimize the risk of bias, Peters et al. (2015) and Ferrari (2015) guidelines for conducting a nonsystematic review were strictly adopted. Nonetheless, our review has some limitations. First, from a methodological standpoint, the number of studies included in our review was somewhat small. In part, this reflects the limited number of available longitudinal studies examining both EF and vocabulary in early childhood. Of course, given the field’s mounting concern regarding publication bias (Kühberger et al., 2014), it is also important to consider that there may be additional, unpublished studies reporting null findings which are not included in the present scoping review. Additionally, this review was also constrained by a specific age range in childhood as well as strict definitions of key constructs. Indeed, language is a complex and multifaceted construct. This means that there are aspects of language development that cannot be captured through measures of expressive/receptive vocabulary (e.g., grammar, pragmatic skills, or communicative gesturing) and as such, this review cannot speak to the developmental link between EF and aspects of early childhood language that extend beyond vocabulary. That said, there is some evidence to suggest that EF is related to an array of linguistic abilities (Blain-Brière et al., 2014; Morgan & Wren, 2018; Woodard et al., 2016). To further our understanding of the longitudinal relation between EF and language more broadly then, there is a need for additional research examining measures of language acquisition outside of vocabulary development.

Second, the examination of external factors that may predict children’s EF and vocabulary outcomes (i.e., model C) was beyond the scope of this review. As such, tertiary variables that may influence the relation between EF and vocabulary were not addressed. There is research to suggest that child-centric (e.g., birth order and temperament) and contextual factors (e.g., school setting, home environment, socioeconomic status, and parenting behaviors) are related to children’s EF and vocabulary development (Blankson et al., 2011; Dixon & Smith, 2000; Finch et al., 2019; Helm et al., 2019; Justice et al., 2018; Madigan et al., 2019; McAlister & Peterson, 2006; Rueda et al., 2005). For example, Blankson et al. (2011) report that environmental stimulation moderated the relationship between EF and vocabulary in a large sample of preschool children. These authors found that the degree to which EF skills related to child vocabulary outcomes varied as a function of how stimulating children’s home environments were. It is possible then that sample demographics and environmental factors also serve as a potential source of variability in the literature whereby the longitudinal association between EF and language may differ as a result of familial access to resources, early childhood education, family composition, etc. (Blankson et al., 2011; Justice et al., 2018; McAlister & Peterson, 2006). Moreover, in introducing Bishop et al. (2014)'s causal models, we presented developmental research that offers some insight into variables that may account for the longitudinal link between early childhood EF and vocabulary (e.g., executive attention and private speech). A detailed examination of these and as well as other potential mechanisms was outside the aims of the current review. However, having verified that there is a relation between EF and language at multiple timepoints across early childhood, supplemental mechanistic research is certainly warranted to identify factors that may underlie this longitudinal association.

Finally, our review only addressed findings from work with TD, monolingual children. A close examination of the literature conducted with atypically developing and/or bilingual child samples may inform the field’s understanding of the relationship between EF and vocabulary or language more broadly. For example, deficits in EF and language are frequently reported among children diagnosed with autism spectrum disorder (ASD). Weismer et al. (2018) found that in comparison to TD controls, school-aged children with ASD exhibited poorer performance on nonverbal EF tasks. However, group differences as a function of ASD status were eliminated after controlling for children’s social communication skills. Weismer et al. (2018) also reported that the association between vocabulary and EF was stronger for children with ASD in comparison to the TD group. Likewise, Diaz et al. (2021) report that there are differences in the longitudinal associations between EF (i.e., inhibitory control and cognitive flexibility) and receptive vocabulary as a function of children’s bilingual/monolingual language status. Although these findings cannot address directionality, they suggest that the relation between EF and vocabulary extends beyond studies of TD, monolingual children and that the examination of bilingual and/or atypical child trajectories may provide additional insight into the association between EF and vocabulary in early childhood.

The purpose of our scoping review was to identify trends in the literature regarding the longitudinal link between EF and vocabulary development based on the existing empirical research. We demonstrated that there is considerable empirical support for the association between EF and vocabulary at various time points in early childhood. However, findings regarding directionality were somewhat less conclusive across studies. Whereas a few studies found evidence for a bidirectional relationship between EF and vocabulary, others reported a unidirectional pathway whereby either early EF predicted later vocabulary size or early word knowledge/production predicted subsequent EF abilities. In part, disagreement across studies may be due to study design factors as direct replications were underutilized in the literature. Additionally, many studies administered verbally demanding EF tasks and as such, differences in performance may reflect variations in children’s non-EF abilities as opposed to their domain-general EF abilities. Identifying sources of variability across study findings provides an avenue for future research to garner insight into the causal nature of the link between EF and vocabulary in early childhood. Such knowledge will ultimately lead to a more nuanced and empirically informed theoretical understanding of how these processes unfold and interact starting in late infancy up through early childhood.

Due to the nature of the current review, ethics approval was not required.

The authors have no conflicts of interest to declare.

This article was informed by research supported by grants R01 HD049878 and R03 HD043057 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) awarded to Martha Ann Bell. The content of this article is solely the responsibility of the authors and does not necessarily represent the official views of the NICHD or the National Institutes of Health.

M.B., in collaboration with M.A.B, formulated the review’s goals and aims. M.B. was responsible for the development and implementation of the selection criteria and search strategy, under the supervision of M.A.B. Finally, M.B. wrote the original draft of the review paper, which was reviewed and edited in collaboration with M.A.B.

Due to the nature of the current review, no data is available.