The development of cooperation and cooperative norm enforcement in children and adolescents: The role of in-group favoritism

Various scholars have discussed the influence of group membership on cooperative behaviors in adult samples. Nonetheless, the developmental trajectories of related biases from middle childhood and early adolescence remain to be explored. Using the one-shot 4-player public goods game and inducing group membership awareness by school affiliation, we investigated the effects of group membership of imaginary partners on cooperation (Experiment 1) and cooperative norm enforcement (Experiment 2) in children and adolescents across fourth (N = 106, Mage = 9.53 years, 57 girls), sixth (N = 109, Mage = 11.46 years, 54 girls) and eighth grades (N = 102, Mage = 13.22 years, 47 girls). In Experiment 1, participants were first-party players and showed higher cooperation with in-group members (i.e., players from the same school) than out-group members (i.e., from other schools); the mediating role of cooperative expectations in in-group favoritism in cooperation was observed only among fourth and sixth graders. In Experiment 2, participants were third-party executors (i.e., could punish either in-group and out-group free-riders), and results showed that fourth and sixth graders were more lenient with in-group violators; eighth graders showed no evident bias in punishment. These findings depict a developmental pattern of decline in in-group favoritism regarding cooperation and cooperative norm enforcement from middle childhood to early adolescence. Cooperative expectations mediated the effect of group membership on cooperation only among younger students, indicating that divergent mechanisms underlie cooperative bias between groups in different grades. The discussions suggest that the understanding of norms of both cooperation and equality developed during this period.