The problem of substance use among older youths is often disregarded in prevention research. The prevailing perception has been that prevention programming is developmentally inappropriate for those who are actively experimenting with substances. This project examines the differential effectiveness of youth-driven adaptations of the evidence-based prevention program, keepin' it REAL (kiR). During Phase I, high-risk youths in a variety of community settings (social, therapeutic, and academic) tailored kiR workbooks/videos to increase the relevance for their peers, older adolescents who are likely to have already initiated drug use. Phase II, discussed here in detail, evaluates the effectiveness of the adapted versions of kiR compared with the original and comparison condition using a quasi-experimental pretest-posttest design with a 6-week follow-up and focus groups. Data suggest that participants receiving the adapted version of the curriculum experienced greater improvement in acceptance and use of substances than youths in the other two groups.