Despite billions of dollars spent by policy institutions and academics, very few programs designed to increase managerial skills among microenterprises are cost-effective. This short paper highlights a mentorship program designed to provide managerial skills to Kenyan microenterprises, and it provides a detailed cost-benefit analysis. For each dollar spent on a treated firm, average profit increases by 1.63 USD; the result stems from both a higher program impact and lower cost relative to existing training programs. Motivated by this increased cost-effectiveness, the study then compares the program to the large literature focusing on “supply-side” interventions designed to increase managerial capacity in small firms, and it highlights particular margins on which mentorship improves on classroom training and also where training should focus.