Background: Participation in extracurricular activities can have positive effects on youth, with greater participation associated with higher academic as well as better socioemotional and behavioral outcomes. Little research has examined differential effects of in-school and out-of-school activities. Methods: This study examines in-school and out-of-school extracurricular activities for 14- to 17-year-olds using a population-based sample of Canadian youth. Associations with socioemotional and academic outcomes, and having tried smoking, alcohol, and marijuana were examined. Results: Weekly participation in both in-school and out-of-school activities were associated with positive and negative outcomes. In particular, youth who participated in out-of-school activities or in both in-school and out-of-school activities had better socioemotional outcomes. Academic outcomes were associated with in-school and out-of-school sports and nonsport activities. Youth who participated weekly in nonsport activities regardless of the context (in-school or out-of-school) were less likely to have tried smoking, alcohol, or marijuana. However, weekly participation in in-school sports was associated with an increased likelihood of failing a course; youth who participated weekly in out-of-school sports were more likely to have tried alcohol. Conclusion: The findings suggest that participation in extracurricular activities, regardless of context, encourage positive youth development.