1. PROJECT SUMMARY Relapse rates among adolescents remain high despite advances in substance use disorder (SUD) treatment. Chronic relapse cycles have high individual costs, such as higher risk of infectious disease transmission and low life satisfaction, as well as downstream societal costs, including healthcare system burden and inefficiencies. Limited adolescent-focused recovery supports represent a critical barrier to sustaining treatment effects, highlighting the critical need to invest in research that contributes to the evidence base of adolescent- focused continuing care and development of adolescent recovery supports. Recognizing the urgency of this research and its potential contributions to the field, the National Institute on Drug Abuse’s (NIDA’s) 2022-2026 Strategic Framework identified developing and testing recovery support strategies as a priority scientific area, with a goal of advancing the science of recovery support. Recovery supports affiliated with youth-serving institutions offer a unique opportunity to provide adolescents with developmentally appropriate continuing care following SUD treatment. Recovery high schools (RHSs) are one such approach, which are specialized schools designed to provide students with therapeutic and peer recovery supports in a learning environment where all students are committed to maintaining recovery from an SUD, cultivating a pro-recovery social network for these adolescents. Using innovative approaches that align with NIDA key focus areas, this project will draw upon data from the only controlled evaluation of RHSs to date to accomplish the following aims: (Aim 1) examine whether RHS attendance following SUD treatment has beneficial effects on long-term recovery outcomes; (Aim 2) identify if and to what extent pro-recovery peer affiliation mediates the proposed relationship between RHS attendance and recovery outcomes; and (Aim 3) assess whether and to what extent the indirect effect of RHS attendance on substance use outcomes via pro-recovery peer affiliation is moderated by perceived social benefits of substance use. Upon successful completion, this project will help NIDA accomplish its goal of advancing the science of recovery support by delivering the expected outcomes: (1) additional evidence supporting RHSs as a continuing care approach; and (2) greater insight into the underlying mechanisms and conditional processes of RHS attendance. This critical knowledge is needed to support the refinement and expansion of RHSs to provide greater and more equitable access as well as inform the development of other continuing care approaches for this underserved population.