We evaluate the impact on youth crime of a welfare reform that tightened activation requirements for social assistance clients. The evaluation strategy exploits administrative individual data in combination with geographically differentiated implementation of the reform. We find that the reform reduced crime among teenage boys from economically disadvantaged families. Stronger reform effects on weekday versus weekend crime, reduced school dropout, and favorable long-run outcomes in terms of crime and educational attainment point to both incapacitation and human capital accumulation as key mechanisms. Despite lowered social assistance take-up, we uncover no indication that loss of income support pushed youth into crime.