This study investigated whether the members of adolescents' peer groups are similar in terms of their school adjustment and whether this homogeneity varies according to peer group type and gender. A total of 1262 peer group members who had recently moved to post-comprehensive education filled in questionnaires measuring their academic achievement, satisfaction with their educational track, school engagement, and school burnout. They also gave positive peer nominations on the basis of which 360 peer groups were identified and categorized as cliques, loose groups, and isolate dyads. The results showed that the members of adolescents' peer groups particularly resembled each other in terms of academic achievement. Moreover, the members of girls' cliques showed greater similarity to each other in terms of their satisfaction with educational track and school engagement than did the members of girls' loose groups. Girls' isolate dyads were, in particular, at risk for low adjustment at school. (Contains 4 tables.)