There is growing awareness of the importance of school building environments for student health, well-being, and even educational outcomes. We ask in this study what role school building heating, ventilation, and air conditioning (HVAC) systems play in shaping student attendance, behavior, and learning. In particular, we extract information from school building inspection reports and link them to education records for public K-12 schools in New York State outside New York City between the 2005-06 and 2018-19 academic years. Using a difference-in-differences approach, we find that improvements in school HVAC system conditions over time reduce student absence, reduce student suspension, and modestly increase student math and reading scores. Heating and cooling system replacements and reconstructions also increase student math achievement. We conclude that investments made now to improve school HVAC systems can benefit not only student comfort and well-being, but also enhance educational opportunity.