The study found that participation in team sports, student government, cheerleading, pep clubs, the performing arts, and academically oriented clubs was generally related to more favorable academic, psychological, and behavioral adjustment; however, patterns of adjustment differed by extracurricular activity. These findings add to a growing literature that shows the importance of school extracurricular activities in positive youth development. Some support was found for the prediction that the link between extracurricular participation and positive adjustment is influenced by association with a prosocial peer group. Data for the study were obtained from the Childhood and Beyond Study, a larger study of activity choice in childhood and adolescence. Because the current study was interested in the consequences of extracurricular participation in high school, it used survey information collected when the youth were in the 9th, 10th, and 12th grades (n=498). Participants lived in three middle-class communities near Detroit, MI. They completed questionnaires that measured involvement in extracurricular activities, school adjustment, academic performance, psychological adjustment, characteristics of the peer group, and risk behavior. The parents of each participant provided information on demographic factors. Gender, grade-level, parents' education, and grade-point average were included as covariates. Participants in any extracurricular activity were compared to nonparticipants on each of the outcomes. Regressions were performed to examine whether perceptions of a prosocial peer group influenced the relationship between time spent in extracurricular activities and indicators of adjustment. 6 tables, 41 references, and appended list of items used in the analysis