This study examined the influence of growth-fostering mentoring relationships on the self-esteem of adolescent female students from affluent communities. Studies have demonstrated that this population of students is susceptible to psychological distress and self-esteem problems, due to perfectionistic strivings and achievement pressures. Specifically, we hypothesized that growth-fostering mentoring relationships (e.g., with teachers and school staff) would be positively associated with self-esteem. Moreover, we expected that this association would be mediated by engagement in purposeful activities. The authors surveyed 207 girls from two independent secondary schools and found support for the mediation hypothesis. Using an ordinary least squares regression approach, the association between growth-fostering mentoring relationships and self-esteem was mediated by youth engagement in purposeful activities. Implications for future research and practice in schools are discussed.