To examine whether trajectories of participation in organized activities during the high school years and beyond (from ages 14 to 20) predicted outcomes at age 21 (externalizing problems, internalizing problems, civic engagement, number of years of education, and perception of physical health), 354 youths (60% girls) were surveyed annually over nine years. Four trajectories were found: (a) "Low and decreasing" (71%), (b) "Moderate and stable" (12%), (c) "High and decreasing after high school" (12%), and (d) "High and increasing after high school" (5%). Results revealed that the predicted outcomes varied according to the different trajectories. Pursuing high levels of activity participation beyond high school was especially beneficial with respect to externalizing problems and educational attainment.