Updating a previous systematic review of the literature, this review summarizes the literature over the last 5 years on the relationship between school-based extracurricular activity participation and academic achievement, substance use, sexual activity, psychological adjustment, and delinquency. The review also considers mediators and moderators of these relationships. This review also discusses recent advances in activity research including participation measurement (intensity, breadth, and duration), person-centered approaches, and an exploration of the overscheduling hypothesis. The review reveals a mixed picture of the relationship between activity participation and these adolescent developmental outcomes. A call for continued exploration into measurement issues, analysis approaches, outcome measures, and causal models of activities and adolescent functioning is made. (Contains 1 table.)