Fast Track Intervention Effects and Mechanisms of Action Through Established Adulthood.

Early preventive interventions can improve outcomes in childhood, but the most effective interventions can continue to deliver benefits through the life course. The Fast Track intervention, a randomized controlled trial for children at risk of conduct problems, has lowered psychopathology, substance use problems, and criminality and elevated happiness at age 25. However, research has not studied whether the intervention's effects continue further into established adulthood. In addition, little is known about the mechanisms through which the intervention may affect adult outcomes. We attempted to answer both questions by simultaneously estimating the intervention's direct effect on adult outcomes at age 31 and the intervention's indirect effects on those outcomes via interpersonal, intrapersonal, and academic competencies gained through the intervention. Participants included the Fast Track intervention (n = 445; 72.4% male) and high-risk control samples (n = 446; 66.4% male). Direct and total effects of random assignment to Fast Track on age 31 outcomes were not significant. However, our analyses showed that Fast Track's improvements to interpersonal and intrapersonal skills in childhood served as catalysts for better life outcomes at age 31. Higher interpersonal skills led to fewer externalizing, internalizing, and substance use problems, reduced criminality and sexual partners, in addition to increased general health and full-time employment. Improved intrapersonal skills led to greater strength. There were no significant indirect pathways via academic skills. Our findings inform understanding of how a childhood preventive intervention can improve adjustment and behaviors into established adulthood.