This study examines the extent to which a third-party policing experiment designed to prevent truancy in disadvantaged adolescents is able to weaken the effect of impulsivity on self-reported antisocial behavior over time. Data are used from the Ability School Engagement Program (ASEP), a randomized controlled trial of 102 high truant youth from Brisbane, Australia who were followed for 2 years postrandomization. We find that ASEP weakened the effect of impulsivity on the diversity of self-reported antisocial behavior throughout the study for those in the experiment. This study provides evidence that an intervention that was designed to prevent truancy has the additional benefit of hindering the relationship between impulsivity and self-reported antisocial behavior variety.