<p>Exposure to particulate matter (PM) in schools significantly contributes to respiratory problems among children found in such learning environments. There is limited information about the health effects of exposure to PM in schools in Rwanda. The aim of this study was to assess the adverse effects of PM on children’s lung function in selected schools in Kigali, Rwanda. The study was conducted in six public primary schools classified as highly or moderately exposed schools based on their proximity to pollution sources. The study involved 107 randomly selected children aged 8 to 15. The study measured the indoor air concentrations of PM_2.5 and PM₁₀ and tested the lung function of school children. Three lung function indicators including forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), and peak expiratory flow (PEF) were measured. Both forms of data were collected during the dry and rainy seasons. Air quality was monitored in classrooms using Purple Air PA-II sensors, and the children’s lung function was measured using a spirometer. Linear regression analysis was used to determine the associations between PM_2.5 and PM₁₀ concentrations and lung function at <i>p</i> = 0.05. The findings showed that the concentrations of PM_2.5 were two to five times higher, and PM₁₀ levels were about two times higher than the World Health Organization’s air quality guidelines. Both PM_2.5 and PM₁₀ were associated with reduced lung function, regardless of the season. The present study shows significant adverse effects of exposure to PM₁₀ and PM_2.5 on the lung function of children in the selected schools. Hence there is the need to take measures to improve air quality and protect the health of school communities.</p>