The present study examined the interactive effects of school norms, peer norms, and accountability on children's intergroup attitudes. Participants (n = 229) aged 5–11 years, in a between-subjects design, were randomly assigned to a peer group with an inclusion or exclusion norm, learned their school either had an inclusion norm or not, and were accountable to either their peer group, teachers, or nobody. Findings indicated, irrespective of age, that an inclusive school norm was less effective when the peer group had an exclusive norm and children were held accountable to their peers or teachers. These findings support social identity development theory (D. Nesdale, 2004, 2007), which expects both the in-group peer and school norm to influence children's intergroup attitudes.