This project draws from youth voices to develop theory about outcomes and change mechanisms in a cross-age mentoring out of school program with urban African American and Latine youth living in low-income communities. With instructors’ supports, African American and Latine mentors (N = 148, ages 14–20) in four U.S. urban, high-poverty communities of color mentored children weekly for an average of 16 sessions, followed by a debriefing session. Researchers used qualitative, participatory methods to elicit mentor perspectives about what made their program impactful. Diverse qualitative data were collected by staff and youth and analyzed thematically. Outcomes adolescent mentors deemed meaningful were 1) developing good character, specifically persistence, leadership and listening skills, patience, respectful collaborations, goal-oriented hopefulness, and more positive racial identities, and 2) building trustworthy, supportive relationships with mentees, peers, and instructors. Mechanisms mentors regarded as generating outcomes were 1) being active agents in program implementation and evaluation, and also contributing knowledge about themselves, and 2) the fulfillment of caring for community children, which youth regarded as a partial remedy for deprivations and injustices their communities experience. Differences in emphasis based on gender are described. Outcomes and generative mechanisms are discussed in relation to youths’ community cultural wealth. Comprehensively empowering youth to co-lead program development, implementation, evaluation and theorizing can improve the fidelity of scientific knowledge to youths’ strengths and priorities, and yield theories of intervention consonant with youths’ cultural wealth.