Consistent with the hypotheses of the social development model, participation in fewer structured and more unstructured activities was predictive of more misbehavior in school and delinquency within this developmental period. That these relationships were predictive, controlling for earlier levels of antisocial behavior, is evidence of activity involvement being linked to social development. There was also evidence that the level of antisocial behavior during elementary school predicted involvement in after-school activities in middle school; i.e., students who exhibited teacher-reported disruptive behavior in the last year of elementary school were more involved in unstructured after-school activities and less involved in structured after-school activities in the first year of middle school. These predictive relationships, however, were small in statistical size. Contrary to social development model hypotheses, there was little evidence that antisocial behavior predicted activity involvement across the transition into high school, after accounting for prior patterns of involvement in activity. Consistent with routine activities theory, involvement in unstructured activity and delinquent behavior in the first year of high school were positively correlated after adjusting for prior levels of antisocial behavior and involvement in structured and unstructured activities. Data were obtained from parents and students in the spring of each project year, and teacher surveys were administered in the spring until students were in eighth grade. 2 tables, 1 figure, and 49 references