Most children do not meet physical activity guidelines, and school-based programs often fail to increase physical activity levels. However, there has been no intervention pairing college mentors with elementary students to date. The purpose of this paper is to report the feasibility and acceptability, both quantitative and qualitative, of an undergraduate-mentored running program designed to increase physical activity in elementary students. A convergent parallel mixed methods design was used to evaluate the feasibility and acceptability of the physical activity intervention for elementary students. Running W.I.S.E. [with Interscholastic Student Engagement] paired college mentors with individual fifth grade elementary school students for bi-weekly running sessions during the school day in early 2020. Quantitative recruitment and retention data were collected and analysed to determine feasibility and acceptability, respectively. Qualitative data comprising letters written by undergraduate mentors to their mentees after the intervention were analysed. Both feasibility and acceptability were achieved. Recruitment and retention rates [100% each] exceeded the pre-defined feasibility and acceptability criteria. Undergraduate mentors were driven to participate by prosocial, passion-driven, and utility motives. Psychosocial mentor/mentee benefits, as well as observed physiological changes among mentees, were cited as outcomes of participation. Undergraduate-mentored running programs a feasible and acceptable means of increasing physical activity in elementary students. Benefits to both mentors and mentees exist and extend beyond physical health into social and mental health, as well.