In the resource-constrained education sector in South Africa, infrastructure deemed temporary or backup elsewhere is used as permanent classrooms, mainly in areas of low income. Temperature and CO2 levels, substantial determinants of air quality, have not been studied across different classroom types, despite their direct impact on children’s cognitive performance and comfort. We measure CO2 and temperature every 11 min in 24 classrooms at two schools in Stellenbosch, South Africa. Container classrooms with and without insulation, mobile (prefabricated) classrooms, and brick classrooms of different configurations are included. Measurements were concurrently sampled over twelve months, across multiple seasons with relevant metadata, including ambient weather conditions. We analyse temperature and CO2 concentrations for classroom types and classroom categories and compare school days with non-school days. The results show that temporary classrooms (container and mobile) have substantially worse thermal environments, even when air conditioning is available. The CO2 concentrations in container classrooms are substantially worse, whereas mobile classrooms have better conditions comparable to brick classrooms. We conclude that container classrooms have the worst temperatures and ventilation, prefabricated classrooms have acceptable ventilation but poor thermal qualities, and brick classrooms have the best thermal environment and ventilation.