Although mentoring programs are increasing in popularity as a preventative intervention strategy for youth, little is known about the experience from the mentor's perspective. In this study, we describe a longitudinal assessment of 41 mentors, including 13 men and 28 women (M[subscript age]?=?21.93?years, SD?=?3.21) working with at-risk youth in a school-based mentoring program. Before starting the program, mentor perceptions, motives, and efficacy were assessed and again after three and six months of mentoring to measure change across time. At the end of the program, mentors evaluated the relationship and rated perceived benefits. Mentors experienced significant changes in perceptions and efficacy across time and changes predicted relationship satisfaction and perceived benefits. Recommendations to support mentors and develop sustainable and satisfying mentoring relationships are provided.