Although most mentoring programs for youth are structured around intergenerational relationships, a growing number of programs rely on cross‐age peer mentoring. Such programs capitalize on the availability of youth mentors to promote positive outcomes in younger peers. This study used a multilevel meta‐analytic approach to estimate the effect size of cross‐age peer mentoring programs and evaluate potential moderators of peer mentoring program effectiveness. Analyses included six studies and revealed a medium‐sized overall effect of cross‐age peer mentoring programs (g = 0.45). Several characteristics moderated effect sizes, with larger effects for programs that were conducted outside of the school setting (i.e., weekend, summer, or in community settings), conducted in urban settings, and had moderate/high levels of adult oversight and supervision. Results highlight the potential benefits of cross‐age peer mentoring for youth. Highlights: Analyses revealed a medium‐sized overall effect of cross‐age peer mentoring programs (g = 0.45).Cross‐age peer mentoring can be an accessible intervention for promoting positive youth outcomes.Peer mentoring programs with moderate to high levels of adult oversight and supervision had larger effects.This study is the first meta‐analytic assessment of the impact of cross‐age peer mentoring programs. [ABSTRACT FROM AUTHOR]