The effects of social group norms (inclusion vs. exclusion vs. exclusion-plus-relational aggression) and school norms (inclusion vs. no norm) on 7- and 10-year-old children's intergroup attitudes were examined. Children (n = 383) were randomly assigned to a group with an inclusion or exclusion norm, and to 1 of the school norm conditions. Findings indicated that children's out-group attitudes reflected their group's norm but, with increasing age, they liked their in-group less, and the out-group more, if the group had an exclusion norm. The school inclusion norm instigated more positive attitudes toward out-group members, but it did not moderate or extinguish contrary group norms. The use of school norms to counteract the effects of children's social group norms is discussed.