Although children are highly vulnerable to higher temperatures and spend significant portions of their time at school, extreme heat events at school locations have not been adequately examined in previous research on social inequalities in the distribution and impacts of heat exposure. We address this gap by conducting the first nationwide study of sociodemographic disparities in extremely hot days at U.S. public schools. Annual frequency of extreme heat days at school locations is measured using both absolute (>90 °F) and relative (> local 95th percentile) temperature-based thresholds, and linked to race/ethnicity, socioeconomic status, and other relevant characteristics of students and schools in the conterminous U.S. Results indicate that racial/ethnic minority students and those eligible for free/reduced lunch are significantly overrepresented in schools with the highest frequency of extreme heat days (top 20 % nationally) compared to White and non-eligible students, respectively, based on the absolute temperature threshold. Similar racial/ethnic disparities are observed in the top 20 % of schools based on the relative temperature threshold, with the exception of Black and Asian students. Multivariable models that control for spatial clustering and contextual factors also reveal racial/ethnic disparities, with significantly higher frequencies of extreme heat days at schools serving Hispanic and American Indian students, regardless of the temperature threshold utilized. These results highlight the urgent need to include school children in future research on social disparities in heat exposure, conduct more detailed investigations in other regions, states, and nations, and formulate interventions and policies that provide equitable protection from extreme heat.