One of the most important aspects of a healthy school--and one that, unfortunately, often falls by the wayside--is indoor air quality. The U.S. Government Accountability Office estimates that more than 15,000 schools nationwide report suffering from poor indoor air quality. According to the U.S. Environmental Protection Agency, schools with poor indoor air quality experience increased absenteeism, decreased student concentration and productivity, and lower student test scores. This article discusses the causes and effects of indoor air pollution in schools and provides guiding principles for principals to ensure optimal indoor air quality in their schools.