Abstract: How does supervision impact worker performance? This paper examines the effects of frontline supervision on the speed and quality of production in a Ugandan data-collection firm. We conducted a field experiment, varying the timing and intensity of supervision among workers, to study the effects of supervision on worker performance. We find that, following increased supervision, workers demonstrate improvements in the dimensions of performance where they were initially weakest. These effects persist, even on days, performance metrics, and tasks that are not directly supervised. Our findings suggest that supervision facilitates targeted on-the-job coaching of workers, which results in economically meaningful improvements in their performance. This underscores the significance of supervisors as conduits for the transmission of tacit production knowledge within organizations.