Mendell, Mark. Indoor Air, vol 23, issue 3, April 2013. This report found that bringing classroom ventilation rates up to the state-mandated standard may reduce student absences due to illness by approximately 3.4 percent. Extensive data on ventilation rates was collected from more than 150 classrooms in California over two years. The study found that ventilation rates varied widely across the districts, within districts, and even within schools, and that portable classrooms, on average, had less ventilation.