Studies show that children who use relational aggression process social information in unique ways; however, findings have been inconsistent and limited by methodological weaknesses. This short-term longitudinal study examined developmental changes in 245 (49% female; ages 8-13) 3rd through 8th graders' normative beliefs about relational aggression and tested the hypothesis that individual and classroom-level norms predict relational aggression 1 year later. Results showed that the transition to middle school was marked by increased approval of relational aggression, and individual norms predicted future relational aggression. Importantly, a contextual model showed that students in peer groups highly supportive of relational aggression became increasingly aggressive. Findings extend social information processing theories of relational aggression to focus on the role of peer group cognitions.