Evaluating the impacts of public school funding on student achievement has been an important objective for informing education policymaking but fraught with data and methodological limitations. Findings from prior research have been mixed at best, leaving policymakers with little advice about the benefits of allocating public resources to schools or how it might best be done. In this study, the authors take advantage of a pilot supplemental funding program in North Carolina that used a quantitative index of educational advantage to select the most educationally disadvantaged districts in the state to receive funding. The targeted districts received supplemental funds of $250 per pupil or $840 per academically disadvantaged pupil for the 2 years of the pilot. Using a regression discontinuity design and multilevel models with extensive controls, the authors estimate that the marginal average treatment effect of the supplemental funding was 0.133 standard deviation units and that the effect on educationally disadvantaged students was 0.098 standard deviation units. The treatment effect represents approximately one third of the difference between the average score in top performing and low performing high schools. (Contains 1 note, 2 tables, and 5 figures.)