Coal is a primary source of both global energy and air pollution. This paper presents the first causal evidence of the impact of pollution due to coal power plant emissions on cognitive outcomes. Our approach combines rich longitudinal student data with a design leveraging year-to-year coal plant emissions, persistent wind patterns, and also plant closures. We find that every one million megawatt hours of coal-fired power production decreases mathematics scores in schools within ten kilometers by 0.02 σ . Gas-fired plants exhibit no such relationship. Our analysis indicates that declining coal use has affected student performance and test score inequality substantially.