Persistent school absence can harm learning outcomes and lead to substantial socioeconomic setbacks. While regional studies have documented the connection between overall school attendance and air quality, the impact of air pollution on chronic absenteeism, which matters most for socioeconomic outcomes, remains unexplored. We address this gap using a national sample of K-12 schools and data for six criteria air pollutants monitored by the U.S. Environmental Protection Agency (EPA). We find a statistically significant and heterogeneous impact of air pollution on chronic absenteeism, even when pollution is below the EPA-recommended thresholds. Using wind direction as an instrumental variable, we find that an additional bad CO, NO2, or PM2.5 air quality day can increase chronic absenteeism by 0.6%, 0.2%, and 0.2%, respectively. These estimates suggest that an additional bad air quality day across the U.S. can increase the number of chronically absent students by up to 54,000 annually. We also document the uneven distribution of the impact on chronic absenteeism across racial, income, and age demographics. With a documented systematic impact of air quality on school attendance, our work adds valuable insights to the ongoing conversation about environmental impacts on education.