Abstract This proposal seeks funding to examine the impact of a 12.5-year long, relationship-based, professional mentoring program, Friends of the Children (FOTC) within the context of an existing multi-site randomized controlled trial (RCT; FOTC versus control). The research trial (The Child Study) was funded by the NIH through the NICHD from 2007-2013. The program has continued through a variety of external funders. Professional mentors (called “Friends”) have continued working with the youth since the project began. Mentors receive extensive training and apprenticeship, and then participate in ongoing supervision, working with a typical caseload of 8 children during elementary school and 10-12 youth during middle and high school. Across the course of the program, youth involved in the program have interacted both with their mentors and with other youth-mentor pairs, becoming part of a community of children and adolescents and caring adults. To the best of our knowledge, there are no published, rigorous outcome studies of a mentoring program that has this combination of program elements. The study is built on the rigorous research program that began during The Child Study (Eddy, et al. 2015, Eddy et al., 2017), which demonstrated the strong adoption and implementation of the FOTC mentoring model. Further, 5 years after the program began, this study found growth in parent’s report of the youth’s behavioral strengths, as measured by increased family involvement, interpersonal strengths and school functioning; positive school behavior; and less externalizing problem behavior in youth randomized to FOTC compared to controls. The proposed study will reengage participants in both intervention and control conditions to conduct end-line (just after actual or estimated high school graduation) and 2-year follow-up evaluations of program impact into young adulthood. The study uses a rigorous RCT design that includes two assessments of all of the active participants in The Child Study (N = 259), a sample of low income, ethnically diverse, at-risk, urban youth. Data will also be collected from caregivers and school, arrest and court records will be collected at the end point. Implementation data collected by FOTC will also be used in the analysis. Young adult surveys will be conducted and arrest and court records collection at the 2-year follow-up (about age 21). Using intent-to-treat analyses, this study will examine program impacts in 3 primary outcomes -- avoidance of involvement in juvenile justice, graduation from high school or obtaining a GED, and delaying parenthood into young adulthood, at the program end point and 2 years later. Further, we will explore whether hypothesized mechanisms of increased social capital mediates the relationships between intervention and outcomes. Finally, we will examine the relationship between various levels of program involvement in FOTC and program impact.