We investigate the male-female gap in principal compensation in state and national data: detailed longitudinal personnel records from 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 $1,450 less annually than their male colleagues with similar characteristics, including experience level and degree attainment, leading the same school in different years. Gaps are present in both base salary and extra duty salary, and are only partially explained by career paths or workplace sorting. SASS analyses show that women make about $1,000 less than men nationally, on average, a gap that even grows larger once accounting for individual and workplace characteristics, teacher-supplied effectiveness ratings, and reported hours worked. The presence of these residual gaps after accounting for many supply-side explanations may signal gender discrimination in school principal compensation. [This paper was published in "Economics of Education Review" v82 Apr 2021.]