Using longitudinal data on 101 sixth-graders who participated in the Pennsylvania Early Adolescent Transitions Study, the following two hypotheses were tested by means of path analysis: (1) the goodness of fit between a child's temperamental characteristics and the temperamental preferences held by the peer group is instrumental in determining a child's peer group relations; and (2) the relation between children's peer relations and adjustment is mediated by the quality of peer social support. Using teacher-, parent-, and self-ratings of children's academic and psychosocial functioning as indices of adjustment, results from several path analyses indicated that children whose temperaments afforded a good fit with their peers' temperamental preferences received significantly more positive peer sociometric nominations and fewer negative peer nominations than subjects whose temperaments did not provide a good fit with the peer group. In addition, peer social support was a significant mediator between the quality of children's peer relations and children's perceived competence. However, children's sociometric nomination scores were more highly related to teacher- and parent-ratings of subjects' adjustment than children's perceptions of peer social support. The results support a person-context fit conceptualization of social competence as well as the importance of peer social support as a mediator between children's peer relations and their perceived self-competence. (Author)