Children under 15 years spend over six hours per day in school buildings and are particularly vulnerable to the effects of poor indoor air quality (IAQ). However long-term monitoring of indoor environmental conditions is limited in Australian schools. This study evaluates IAQ in ten Australian school classrooms in the temperate settings of Victoria. Temperature, relative humidity, CO2 concentration, PM2.5 and PM10 were monitored over a period of one year. The temperature and relative humidity values in the monitored classrooms ranged between 18.7°C and 23.8°C and 44–63 RH%, respectively, indicating that the conditions have been mechanically controlled. The average air change (ACH) rates in the 10 school classrooms varied considerably (range: 0.7–4.83 ACH). The ventilation rates ranged from 1.6 Ls−1 to 11.5 Ls−1 per person with 7 out of the 10 classrooms showing ventilation rates below the recommended minimum. This study points to the need for increasing ventilation rates in classrooms.