In this paper we study an alternative approach to reduce the expansion of criminal organizations: preventing gang recruitment at schools, where criminal organizations commonly target children. To do so, we exploit the staggered implementation of a preventive program in El Salvador that increased anti-gang recruitment campaigns by police patrolling at schools. We show that by focusing on schools, the use of police officers as a preventive measure can reduce gang recruitment at an early age, having positive long-term effects on children’s human capital and potentially reducing gangs’ revenues. In particular, we show that children at key ages for recruitment are significantly less likely to drop out of school and join gangs. Using administrative data from field informants, we find that immediately after the start of the program, gang recruitment declined by 50% and that children are less likely to be detained in juvenile centers due to gang-related crimes. In turn, these outcomes reduce the likelihood that children become involved in a cycle of crime within organized crime networks. We find that affected children are less likely to be incarcerated for gang-related crimes in adulthood. As a result of this decline, we find evidence that gangs’ main business, extortion, is affected in the long run. By addressing a root cause of future criminality, this policy effectively limits gang expansion and decreases revenue streams, as they have less labor to perform their activities.