The juvenile justice system is charged with the welfare of the children it serves, yet less is known about the prosocial behaviors of adolescent youthful offenders. This study identifies patterns of prosocial behavior for 7 years among serious adolescent offenders, the correlates of each pattern, and associated patterns of secure placement. Using 7 years of monthly data from the Pathways to Desistance Study (N = 1,354), we used group-based trajectory models to identify longitudinal patterns of positive youth behaviors related to school and work among serious adolescent offenders and a joint trajectory model to assess the relationship between trajectories of institutional placement and positive youth behaviors. Four groups were identified that demonstrated a high, low, medium, and dips-then-rises likelihood of gainful activities throughout the study period. Gainful activities were negatively associated with risk for delinquency across multiple domains. Juvenile justice interventions should consider prosocial promise in addition to risk for delinquency.