Despite increased attention on girls’ delinquency, evidence-based interventions have been largely lacking. We aim to (a) describe the design and implementation of a gender-specific program for juvenile justice-involved girls and (b) present prospective data on three cohorts of participants. Fifty-two girls were enrolled in the program called the Girls Advocacy Project (GAP). Key risk and protective factors were identified based on existing literature and assessed. Over time, youth reported greater resilience and self-efficacy; fewer risk behaviors, including violence, crime, and substance use; and decreased distress (e.g., depression, anxiety, and anger). Hypothesized program mechanisms and recommendations for future research are discussed.