There is a trend of installing air conditioning systems in public primary schools that are currently naturally ventilated in Vietnam. A previous study conducted by the authors provided evidence that there is limited need for air conditioning in Vietnamese mid-season and the hottest season. In this study, the authors investigated thermal comfort and users’ perceptions in three primary schools in Ho Chi Minh City during the hottest season (April 2016) and the coldest season (December 2016 – January 2017). In-situ spot and long-term measurements were recorded. Questionnaires were completed by 3,960 children (age range from 8 to 11 years) and the teachers to inform the study about their experiences and the extent of their interaction with the building in 97 free-running classrooms. The results were analysed by correlating the conditions measured and the comfort mean votes. The neutral temperatures were respectively 31.7°C and 31.1°C for the hottest and coldest seasons. Children were observed to tolerate higher thermal comfort condition than the recommended values in the standards. Compared with the results of the hottest season, the thermal sensation mean vote reduced from (0.29) to (0.12) when the decrease of the mean temperature was from 33.3°C to 31.8°C in the coldest season. The temperature of 33°C was proposed for the overheating benchmark The results indicated that Vietnamese children adapted to hot climate and had higher thermal comfort tolerance than adults. Preliminary findings suggest that it is unnecessary to use air conditioning system all year round. These findings could help and encourage architects and engineers to deliver schools reaching acceptable comfort levels without the need of air conditioning system.