["Journal of Community Psychology, Volume 54, Issue 6, August 2026. ", "\nABSTRACT\nThis manuscript describes the (1) development of the “DiscoverU” afterschool mentoring program and (2) formative evaluation of its feasibility, acceptability, and initial impact on adolescents' physical activity (PA), interpersonal skills, and social connectedness. We used a convergent mixed‐methods design with quantitative data from adolescents (n = 32) and qualitative data from adolescents (n = 14), mentors (n = 14), facilitators (n = 3), and school staff (n = 3). We assessed pre–post changes physical activity, mindful eating, and social‐emotional skills with paired Wilcoxon tests and used content analysis to identify themes. DiscoverU was highly acceptable and demonstrated initial impacts on PA days/week, peer cooperation, and social connection. Qualitative data indicated adolescents' experience with mentors was important to these outcomes. However, feasibility was limited by inconsistent attendance with 44%–52% of adolescents receiving the intended dose. DiscoverU's novel use of mentoring to integrate physical and mental health promotion was well‐liked by all involved parties. Strategies to enhance consistent adolescent attendance are needed to increase program feasibility.\n"]