A numerical study has been carried out to predict the indoor air quality and thermal comfort in a classroom with a low ventilation rate. Four different air supply methods were used: Displacement ventilation, well-mixed ventilation, and two types of low-wall-diffuser ventilation. The airflow pattern, predicted percentage of dissatisfied occupants, percentage of dissatisfied people due to draught, CO2 concentration, and percentage of dissatisfied people due to indoor air quality were determined using a program based on a k-Îµ turbulence model. It was found that the secondary flow generated by the buoyancy effect produced by the pupils in the room is much stronger than the primary flow supplied from the diffusers. As a result, the overall ventilation effectiveness and thermal comfort are similar under the four air supply methods, except in the region near the diffusers. Supplying fresh air at a lower level (near the floor) may cause draughts. For an acceptable perceived indoor air quality, the ventilation rate should be increased to meet the requirement stated by ASHRAE Standard 62-1989. Â© 1993, Sage Publications. All rights reserved.