Adolescent problem behaviors are costly for individuals and society. Promoting the self-regulatory functioning of youth may help prevent the development of such behaviors. Parent-training and family intervention programs have been shown to improve child and adolescent self-regulation. This study helps fill gaps in knowledge by testing for indirect effects of the Common Sense Parenting (CSP) program on reduced substance use, conduct problems, and school suspensions through previously identified short-term improvements in parents’ reports of their children’s emotion regulation skills. Over two cohorts, 321 low income families of 8th graders were enrolled and randomly assigned to either the standard CSP program, an adapted CSP Plus program, or a minimal-contact control condition. Pretest, posttest, 1-year follow-up, and 2-year follow-up survey assessments were completed by parents and students with 94% retention. Intent-to-treat multivariate path analyses were conducted. Neither intervention had statistically significant total effects on the three targeted adolescent outcomes. CSP, but not CSP Plus, had statistically significant indirect effects on reduced substance use and school suspensions at the 1-year follow-up as well as conduct problems and school suspensions at the 2-year follow-up through increased child emotion regulation skills at posttest. Findings provide some support for emotion regulation as one pathway through which the intervention was associated, indirectly, with reduced substance use, conduct problems, and school suspensions among at-risk students over the high school transition.