Killen, Elenbaas, and Rutland [this issue] report on an impressive line of research, which examines reasoning about social exclusion and denial of resources. By merging perspectives from moral development, and more specifically social domain theory, with research on intergroup theory, the research in social reasoning development (SRD) has led to new and important findings in children's judgments of social experiences among groups. These findings are important for understanding societal level social issues as well as moral development. Bias that appears in adulthood may begin in childhood. Understanding the roots of bias is important for understanding social injustice, and as the authors show, efforts to address bias in childhood can have some success.

The target article does an excellent job of reviewing research on children's reasoning about justice in intergroup situations. One of the strengths of this line of research is its focus on children's reasoning. In this commentary, I hope to add to the discussion of the ways that children develop in their judgments about intergroup justice by commenting on the ways that children develop and use the information available to them to come to their judgments, both biased and just.

Judgments of intergroup situations involving fairness require the consideration of principles of justice as well as contextual information regarding group membership. Consistent with social domain theory [Smetana, 2006, 2013; Turiel, 1998, 2002], Killen et al. suggest that children have a concept of fairness very early, confirmed by extensive research [Smetana, 2006, 2013; Turiel, 1998]. For example, starting in early childhood, there is a strong aversion to inequality [Fehr, Bernhard, & Rockenbach, 2008] so strong that children may discard a resource rather than provide unequal resources [Shaw & Olson, 2012]. Although issues of justice are prominent for children, conventional issues having to do with group norms are also involved in intergroup interaction. Social domain theory research shows that children (and adults) judge moral issues differently than conventional issues involving group norms. Killen et al. focus on the application of fairness judgments to intergroup situations, which invoke conventions. By examining places where moral and conventional issues intersect, Killen et al. have brought the research closer to the complex social issues that challenge people in daily life.

The work done by Killen et al. and others indicates that measuring reasoning is key to understanding moral development, and this may be especially true in intergroup settings where stereotypes influence judgments about groups. This is in part because judgments change dramatically with new information [e.g., Killen, Mulvey, Richardson, Jampol, & Woodward, 2011; Killen & Stangor, 2001]. Although in past research [Damon, 1977], it was found that young children were only capable of using strict equality to distribute resources, more recent research shows that they do consider relevant information like the merit and needs of recipients. Even among young children, recent research finds that children can account for some additional contextual information when judging fairness, though they do so with more facility as they get older [McCrink, Bloom, & Santos, 2009]. For example, Baumard, Mascaro, and Chevallier [2012] showed that young children (ages 3-4) are capable of using information about merit to distribute goods. Other research shows that with age children are able to consider more information when making judgments, an indication that judgments change with age in part because of cognitive development.

Thus even young children consider more than strict fairness when they make judgments about exclusion and distributions, and their judgments evolve when they are presented with new information. Information about groups is necessary in order for bias to become evident. The child has to identify the group members as having common characteristics (including generalizations that may be inaccurate) in order to place an individual in the group. In addition, the children may also consider characteristics of the group that could be related to the issue of fairness (like needs, interests, merit and abilities). For example children sometimes make assumptions about others' needs or merit based on their group status, and this can lead to bias.

The evidence that children exhibit bias is convincing. For example, they allocate more resources to their own ingroups [Renno & Shutts, 2015]. It is also clear that they, like adults, sometimes presume information based on group status rather than based on specific information about individuals. In Renno and Shutts' study, they found that young children's ingroup bias was associated with a presumption that the ingroup members (both racial groups and gender groups) would be more willing to help them. Therefore it seems that even young children have assumptions (about helping in this case) that indicate that they are using ancillary information to make judgments. Children who exhibit bias are balancing more than concerns with strict equality, and they may be reasoning about the characteristics of groups.

In middle childhood, reasoning about intergroup relations becomes more complex as children develop more sophisticated understandings and assumptions about groups. McGillicuddy-De Lisi, Daly, and Neal [2006] found that in middle childhood, white children considered race when rewarding students for artwork. They provided more resources to an African American child for artwork than they did for artwork done by a white child; however they awarded more to a needy white child than a needy black child. The authors interpret this as evidence of aversive racism: having low standards for black children's achievement while being more sympathetic to needy white children. It seems that the children had assumptions about the abilities and needs of the artists that were based on their race. Although the assumptions are based on stereotypes that are inaccurate, they are more complex for older children, entailing negative assumptions that lead to both more and fewer resources. The children may not have been aware of their bias, but even implicit bias requires assumptions, which can be logical if the premise is accepted.

Assumptions about groups are not limited to outgroups and research also shows that norms can also be detrimental to ingroup members (including the self). In fact some research has shown that some low-status groups can sometimes favor the dominant group [Newheiser, Dunham, Merrill, Hoosain, & Olson, 2014]. This may be because stereotypes are associated with assumptions about both outgroups and ingroups.

Given that content and complexity of stereotypes change with age, it is no surprise that children's associated judgments about both outgroups and ingroups also change. Conry-Murray [2015] found that younger children (ages 6 and 8) were more likely than older children (age 10) and adults to judge that unfair distributions were acceptable, but only when the distributions were related to gender norms. This effect was consistent across children of both sexes and applied when both outgroups and ingroups received more resources. Children, especially young children, approved of unequal distributions, even when the distributions harmed their own sex. This finding was recently replicated using different resources, including resources that were easier to quantify so that the inequality would be more salient. Children at ages 7, 9, and 11 again approved of unequal distributions when the items were gendered, regardless of whether boys or girls received more/better items [Conry-Murray, 2016]. In both studies, adults judged that unequal treatment was unacceptable whether it was consistent with gender norms or not.

In order to understand why the younger children were more biased, it is necessary to examine their reasoning, which may be based on stereotypical information. One of the characteristics of groups that is associated with stereotypes is preferences or personal choices. Personal choice is very important to children [Lagattuta, Nucci, & Bosacki, 2010] and yet Conry-Murray [2015] found that children often assumed that all girls and all boys would prefer to receive gender-typical resources, and further, this belief predicted judgments that it was acceptable to give these groups different, and even unequal, gifts. This effect was found across ages, indicating that even the youngest (age 6) may have been considering group status and associated presumed preferences, and drawing conclusions about fairness based on that information. Older children were less likely to presume that all children's preferences were linked to their gender, and they were more critical of unequal gendered distributions. Perceptions that all recipients received gifts they liked predicted evaluations that the distributions were acceptable, even controlling for age.

When there are no assumptions that provide a reason for unequal treatment, children endorse fairness over social norms [Theimer, Killen, & Stangor, 2001]. This can be seen even in studies of young children. For example, Conry-Murray and Turiel [2012] found that children judged that personal choice should be prioritized over gender norms, when they made judgments about a story that portrayed a child who had an atypical preference (e.g., a boy wants to wear a ballet costume). This is evidence that young children use preferences to judge distributions, and responses seem to depend on their assumptions (or knowledge) about those preferences. When preferences are made explicit and are not presumed from a stereotype, children are less likely to be biased.

The sensitivity to a variety of preferences seems to increase with development [Biernat, 1991]. For example, Killen, Rutland, Abrams, Mulvey, and Hitti [2013] found that adolescents were more likely to note preferences that differed from their group expectations as compared to children in middle childhood. Further, adolescents distinguished between their own preference and preference of the group.

Given this, and the fact that adolescents are often focused on justice, why do adolescents continue to exclude others? Killen et al. [2013] suggest that norms become more complex with an increased capacity to consider conflicting information, but they do not necessarily become more flexible. This may be in part because as children grow they also may become more sensitive to the repercussions of defying norms. Studies have shown that even young children consider that defying norms can lead to embarrassment and that people who break norms may get teased. In one study [Conry-Murray, 2013], children advocated for a child to make an unconventional choice when he or she was in private or a supportive environment, but when he or she was in public with traditional norms, children were less likely to advocate that the characters follow their choices. However, older children were more articulate in stating that the reason they advocated changing gender-related behavior to be consistent with norms had to do with concerns about how others would treat someone who expressed an unconventional desire. If older children and adolescents are more sensitive to repercussions for defying norms it may be because they understand the complexities of group function better [Killen & Stangor, 2001]. This may lead them to feel increasing pressure to conform to norms, and they may respond with increased exclusion, as is the case with exclusion based on sexual orientation [Horn, 2006].

Finally Killen et al. point out that some information about groups may be especially difficult to understand, particularly for young children with little experience in the world. They note that with age children are more sensitive to the idea that a group can be a ‘‘habitual target'' [Killen et al., this issue], which in itself is an additional injustice. In this study reported in the target article [Elenbaas & Killen, 2015], researchers asked children to distribute essential resources (e.g., hospital supplies), so that preferences would be less influential. Children had difficulty recognizing that some groups routinely received fewer resources than others. It may be difficult for children to conclude that a group has been targeted systematically unless the child has had repeated experience with this kind of injustice. This is a conclusion that takes experience with the injustice over time, and even then, the knowledge of these systematic injustices may be slower to build for members of groups who are not targets.

Information about the experiences that targets of bias have may be hard to understand for children and adolescents in dominant groups, and this is compounded by the fact that cross-group friendships decline with age. Cross-group friendships are an opportunity for children in dominant groups to get more accurate information about the experiences of those who may be habitual targets, and less contact with outgroup members means fewer opportunities to correct inaccurate assumptions about those groups.

Killen et al. should be applauded for examining commonalities in the way children reason about many different social groups including groups based on gender, race, ability status and sexuality. However, it is also important to acknowledge that the content and context of stereotypes presents different challenges for different groups. For example, Renno and Shutts [2015] found that social preferences based on gender emerge earlier than those based on race. This may be because of the different meaning that gender is given in many cultures today. Diesendruck, Goldfein-Elbaz, Rhodes, Gelman, and Neumark [2013] found that children see gender as a natural-kind category that is fixed, objective and natural. Adults are more willing to state that sex differences are natural and immutable [e.g., Sax, 2005], and therefore children may have special difficulty challenging these notions compared to groups whose presumed qualities are seen as more transient. For example, adults may be more willing to state that racial differences are not natural and immutable. Therefore the information that is available about gender and race can differ.

Still, correcting assumptions about race may also be difficult. Race is seen as a taboo topic for many white parents. Some research has found that 75% of white families with kindergarteners said they almost never discussed race with their kids, while only 25% of nonwhites said this [Brown, Tanner-Smith, Lesane-Brown, & Ezell, 2007]. For children in white families, this taboo may inhibit discussion and make bias more underground.

Children's tendency to overgeneralize categories may also differ by group, given that some groups are more visibly different or are treated differently more often, encouraging children to construct those group categories as more inflexible. Children's tendency to overgeneralize categories like gender [Levy, Taylor, & Gelman, 1995; Taylor, 1996; Taylor, Rhodes, & Gelman, 2009] may lead them to believe that some groups' characteristics are less flexible than others, given the frequency and strength of information about groups that is available to children. The visibility and salience of information about groups can differ in different cultures.

Bias affects people across cultures, but different groups are the target of bias in different cultures [Quintana, 1998]. Culture can provide children with information about groups and different cultures may emphasize ingroup variability more than others. Rhodes and Gelman [2009] found that children from a more conservative part of Michigan remained inflexible about gender norms for longer than children from a more progressive community near a university. This may be a result of being exposed to more variability in regard to gender. Other research also shows some differences in the ways children reason about gender norms. Conry-Murray, Kim, and Turiel [2015] found cultural differences according to which gender norms were endorsed, with children in purportedly more traditional cultures like that of South Korea judging that gender norms are less flexible than American children. In both studies, children in more conservative communities remained inflexible about gender for longer. It may be that cultures where norm violations are more common and accepted provide children with experiences consistent with more flexible orientations toward group conventions.

The content of specific beliefs can also differ in different cultures in ways that can encourage acceptance or exclusion. Quintana [2007] suggested that children in Guatemala showed different beliefs about race than children in the United States. He noted that ‘‘Indígena children opined that a person could change racial group from Indígena to Ladino by changing his or her way of life. In sharp contrast, children in the United States viewed racial differences as genetic or immutable'' (p. 7). Cultural beliefs that group differences are immutable may make it more difficult for children (and adults) to challenge assumptions about groups.

SRD research has started to investigate inventions that appear to be very effective. Cross-group friendships seem very promising. In one study, just hearing about cross-group friendships helped reduce exclusion. Therefore, it may be useful to develop interventions to encourage cross-group friendships. However, some research has shown that some forms of cross-group contact can lead to increases in bias. Moody [2001] found that more diverse schools had more segregation, and Stephan [1991] found that school desegregation led to less prejudice in some cases, but more frequently, white students became more prejudiced. Without opportunities to address inaccurate or overgeneralizations about outgroups, people who only encounter an outgroup superficially may increase their bias. It seems necessary to have substantive interaction between members of different groups in order for inaccurate information to be corrected.

Other research indicates that adults' behavior sometimes supports bias formation. Adults play a role by making these group differences salient, sometimes too salient. Hillard and Liben [2010] found that a classroom where teachers emphasized gender for just a few weeks led to children being more biased. Children construct ideas about groups based on what they observe in the environment even without direct messages. Patterson and Bigler [2006] showed that salient features of the environment like T-shirt colors provided cues to children that groups differ and led to greater ingroup bias. Given that messages about some groups are pervasive in advertising, clothing, and media, even when parents and teachers promote messages of equality, children may infer that the groups are more different than similar.

Future research expanding upon the SRD model should continue to examine interventions that address both reasoning and the ways that norms are constructed and maintained in ways that affect intergroup relations. In addition, more research is needed to examine whether long-term effects of interventions are able to affect people into adulthood.

Clearly experiences affect the ways both children and adults construct their knowledge of groups. Killen et al. have found in some studies that girls were more sensitive to injustice [e.g., Horn, 2006; Theimer, Killen, & Stangor, 2001] and that minority children in the United States were less likely to accept injustice. More research needs to be done to understand the mechanism behind these findings. It may be that experiencing injustice as a victim leads to a moral identity that compels a person to fight that injustice, or it may lead to a more targeted sensitivity to certain types of information, but more research is needed to understand how this works.

Killen et al. have contributed a large body of research that shows that children care about fairness and about personal choice, even in situations related to group norms like those regarding gender, and that fairness and personal choice can be drawn upon to help confront inaccurate assumptions about groups and to help construct group norms of acceptance. Exclusion and unfair distributions of resources that target entire groups are doubly unjust, because they are unfair when they happen to any individual, but targeting people based on group membership is itself another injustice. The work Killen et al. have done on this issue is therefore extremely important and they are to be commended for investigating the roots of bias and for their efforts to address these injustices.

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