A typical K-12 classroom holds 25-30 students in a room sized for 22 to 28 occupants per ASHRAE 62.1. The ventilation rate per student is fixed by the system design; the actual delivered fresh air depends on whether the HVAC runs, whether unit ventilators have been turned off by teachers seeking quiet, and whether windows can be opened.
Three studies are commonly cited. Haverinen-Shaughnessy et al. tracked classroom CO2 and student performance on standardized tests across 100+ classrooms and found significant correlations between ventilation rate and math/reading scores. Shendell et al. documented a 10-20% increase in student absences in classrooms with persistently elevated CO2. Wargocki et al. ran controlled-exposure interventions and saw similar effects on attention and task completion.
The interventions are well-established: EPA's IAQ Tools for Schools framework gives a structured approach; key moves are verifying that unit ventilators are operating, replacing filters on schedule, and adding portable HEPA purifiers in chronically under-ventilated rooms. Demand-controlled ventilation in newer schools eliminates the "off all summer, blasted all morning" pattern.
For Terrestream in a school context, the deployment pattern is one sensor per classroom (or one per zone if the HVAC is grouped), with dashboard notifications at 1,500 ppm CO2. Time-of-day patterns identify which classes drift highest (typically the afternoon math class right after lunch). Year-over-year tracking lets facility staff see whether HVAC retrofits actually delivered the promised improvement.
