2020 No https://doi.org/10.1016/j.buildenv.2020.107003 Kabirikopaei, Adel North America Experimental Exposure Study Students Elementary (K-5) Middle/Jr High (6-8) High School (9-12) Ventilation rates Carbon Dioxide (CO2) Ventilation rate Carbon dioxide (CO2) Classrooms Uncertainty Occupied space CO₂ concentrations were monitored seasonally in 220 Midwestern classrooms to compare methods for estimating ventilation rates. Uncertainty varied by method, system type, and CO₂ sensor accuracy. Findings guide improved air quality monitoring in schools.