We explored the effects of 3 group features (i.e., status, cohesion, and ethnic composition) on socialization processes of aggression in early adolescents' natural peer social groups. Gender differences in these effects were also determined. A total of 245 seventh-grade individuals belonging to 65 peer groups were included in the analyses. All 3 group features moderated the strength of group socialization on physical aggression with the exception of group status on girls' physical aggression. Stronger socialization of physical aggression occurred in higher status, more cohesive, or ethnically more homogeneous groups. In contrast, only group cohesion moderated the strength of group socialization on social aggression among girls. These findings suggest that somewhat different processes may be involved in peer group influences on different forms of aggression. Future intervention and prevention efforts for adolescent aggression should consider peer group membership and group features simultaneously.