The authors examined the relations between participation in a range of high school extracurricular contexts and developmental outcomes in adolescence and young adulthood among an economically diverse sample of African American and European American youths. In general, when some prior self-selection factors were controlled, 11th graders' participation in school clubs and organized sports was associated with concurrent indicators of academic and psychological adjustment and with drug and alcohol use. In addition, participation in 11th grade school clubs and prosocial activities was associated with educational status and civic engagement at 1 year after high school. A few of the concurrent and longitudinal relations between activity participation and development were moderated by race and gender. Finally, breadth of participation, or number of activity contexts, was associated with positive academic, psychological, and behavioral outcomes.