We investigate the male-female gap in principal compensation in state and national data: detailed longitudinal personnel records from the state of Missouri and repeated cross-sections from the nationally representative Schools and Staffing Survey (SASS). In both data sets, we estimate substantively important compensation gaps for school leaders. In Missouri, female principals make approximately $1,400 less annually than their male colleagues with similar characteristics leading the same school in different years. SASS analyses show that women make about $900 less than men nationally, on average. These gaps are only partially explained by sorting, career paths, and other labor supply-side mechanisms, suggesting that gender discrimination contributes to male-female pay differences in school leadership.