This study explores human exposure to harmful dust when antidust chalk is used for teaching, as well as dust particle size distribution and how chalk dust affects indoor air quality. In this study, a classroom with 5 ventilation modes was selected. A dust size analyzer and a scanning mobility particle sizer were employed to measure the mass concentration and particle size distribution of chalk dust based on the frequency of chalk use during classes. The results indicate that antidust chalk can generate considerable quantities of dust particles and substantially increase the mass concentration of dust in the proximity of the chalkboard. Approximately 15% of observed chalk dust particles were respirable and high concentrations of chalk dust deteriorated the indoor air quality. Moreover, chalk dust was the primary source of indoor coarse particles. Mechanical ventilation resuspended the settled chalk dust particles, thereby increasing the mass concentration of airborne dust. Using antidust chalk generates coarse, fine, and ultrafine particles, particularly when cleaning the chalkboard. The best ventilation mode to reduce dust accumulated in the chalk teaching classroom was to open doors and turn on ceiling fans. Wearing face masks and increasing distance between seats and blackboard can also prevent teachers and students from chalk dust hazard. The results of this study should serve as a reference for improving indoor air quality and protecting teachers and students from harmful dust particles in classrooms.