The purpose of this study is to investigate the actual conditions of the indoor environments within public school classrooms and to obtain fundamental information regarding their ventilation design. Field surveys on indoor air quality were conducted at two public elementary schools in Tokyo, equipped with air-conditioning systems. School-A is equipped with heat-exchange ventilation, while School-B does not contain a ventilation facility. The study revealed that School-A has proper indoor air quality and an appropriate thermal environment. However, inconsistencies in the operational methods of the ventilation system were found, and thus, it is necessary to convey the appropriate operation methods to achieve the system's full advantages. The indoor air quality and thermal environment in School-B varied among classrooms. For example, the CO2 concentration was at a suitable value owing to the opening of windows during cooling; however, a large heat load was generated.