We examined the linear and nonlinear relations between breadth of extracurricular participation in 11th grade and developmental outcomes at 11th grade and 1 year after high school in an economically diverse sample of African-American and European-American youth. In general, controlling for demographic factors, children's motivation, and the dependent variable measured 3 years earlier, breadth was positively associated with indicators of academic adjustment at 11th grade and at 1 year after high school. In addition, for the three academic outcomes (i.e., grades, educational expectations, and educational status) the nonlinear function was significant; at high levels of involvement the well-being of youth leveled off or declined slightly. In addition, breadth of participation at 11th grade predicted lower internalizing behavior, externalizing behavior, alcohol use, and marijuana use at 11th grade. Finally, the total number of extracurricular activities at 11th grade was associated with civic engagement 2 years later.