Ventilation rate, a fundamental aspect of indoor air quality, plays a crucial role in maintaining a healthy and comfortable indoor environment. Between 2016 and 2022, continuous measurements of temperature, relative humidity and carbon dioxide (CO2) were conducted from 138 rooms distributed over 48 schools in the Southwest Region of the United States. We have developed a novel approach that simplifies the extraction and analysis of information pertaining to ventilation performance from CO2 time series. We employed decay, build-up and steady-state methods for estimating ventilation rates, including room dimensions and occupancy information. The results were then compared to other indoor environmental quality indicators, building characteristics, HVAC types and student absences to investigate possible associations. This study presents an in-depth analysis of how utilizing a variety of building data sources can enhance the understanding of ventilation performance in schools and its impact on pupils.