This study examined (a) growth curves of youth participation in sports, performance and fine arts, and youth clubs throughout the high school years and (b) the associations between a series of predictors and the initial participation rates and growth over time. The predictors included individual, friend, and family factors. The moderating effect of youths' gender was also examined. Study participants were 272 youths (55% girls, M[subscript age]=12.4 years) and their parents. The predictors were assessed in Grade 6 and were based on reports by youths, parents, teachers, and classmates. Participation in organized activities was assessed annually from Grades 7 to 10. Altogether, the findings revealed that participation in sports, performance and fine arts, and youth clubs remains stable across the high school years. However, interindividual differences were found in the participation growth curves. This variation was predicted by individual, friend, and family factors, mostly with respect to sports activities.