Annual survey data on 776 students from sixth through ninth grade were used to examine the relationships among after-school activities, misbehavior in school, and delinquency. The social development model hypothesizes that antisocial behavior in one developmental time period leads to less involvement in activities and interactions that have positive socializing influence in the next developmental time period. Although the overall correlations between structured activities and both misbehavior in school and delinquency did not indicate strong protective influences of structured activities, results of a cross-lagged model that adjusted for prior activity and behavior patterns provided support for the hypotheses. However, antisocial behavior did not predict involvement in activities across the middle school to high school transition. Consistent with routine activities theory, unstructured activity involvement and delinquent behavior in the first year of high school were positively correlated after adjusting for prior levels of antisocial behavior and structured and unstructured activity involvement. (Contains 1 table, 1 figure and 1 note.)