Drawing on social identity theory, this study explored the impact of the peer group on childhood bullying. Participants were 351 students, aged 8 to 13 years. Involvement in bullying, friendship group membership, norms of particular groups, and intra-group positions (prototypical vs. peripheral) were determined using peer reports. Results revealed within-group similarities in bullying behaviors. In addition, bullying was found to be greater when it was endorsed by group norms and when children were prototypical vs. peripheral members of bullying groups. The implications of the findings for the conceptualization of childhood bullying are discussed.