Sport-based positive youth development (PYD) programs are recognized as important contexts for promoting life skill development and transfer, especially among socially vulnerable youth. Past research has examined the role of social agents (e.g., coaches, staff, parents) in life skill development and transfer. Although peers are identified as a critical social agent in sport-based PYD contexts, little English-speaking literature has examined the influence of peers on youth’s life skill outcomes. This study examines multiple peer influences contributing to life skill outcomes among 483 youth involved in a sport-based PYD program. Cohen’s d demonstrated improved self-control, effort, teamwork, social competence, and transfer of learning outcomes from pre- to post-program. Using a series of hierarchical linear regression models, results demonstrate the degree of life skills among peers in one’s group, the youth’s relative life skills within their group, and the number of friends in one’s group predicted life skills scores at posttest after controlling for pretest scores and demographics. These findings point to the importance of peers as significant social influences contributing to youth’s life skill outcomes in a sport-based PYD program. Sport practitioners can intentionally promote youth development through facilitated group processing, optimal peer group composition, and autonomy supportive staff practices.