Installing air filters in classrooms has surprisingly large educational benefits (2020)

Effect Size and Educational Impact

• Commenters translate the paper’s ~0.2–0.3 standard deviation test-score gains as fairly modest percentile shifts (e.g., 50th → ~55th), not transformational leaps.
• Several argue that large, rapid test-score jumps from a single intervention are inherently suspicious and likely to shrink with better data or replication.

Health, Immunity, and Infection

• Many see a straightforward mechanism: cleaner indoor air → fewer respiratory infections/allergy flares → more attendance and better concentration.
• Others raise immunity-development concerns (hygiene hypothesis, “old friends” hypothesis), but the thread concludes the immune story is complex and unresolved rather than a clear argument against filtration.
• Multiple anecdotes: N95 use and classroom/daycare filtration strongly reducing colds and severe illness.

What Are Filters Actually Doing?

• Distinction between:
  • Particulate filtration (MERV 13, HEPA) for PM2.5, pollen, pathogens.
  • Activated carbon for VOCs and odors (requires substantial carbon mass; many consumer “carbon” filters may be underpowered).
  • CO₂ reduction, which typically needs ventilation, not filters.
• Some note UV-C as an alternative for disinfection, with caveats about safety and design.
• Practical advice appears: MERV 13 often optimal for throughput vs resistance; CR-box–style setups and portable HEPA units discussed.

Quality of the Underlying Study

• Several posts, referencing statistical critiques, argue the paper is weak:
  • Driven by a single breakpoint and questionable linear trend.
  • Non-random assignment (within 5 miles of a gas leak), short time window, uncertain filter usage, no detected gas pollutant to remove.
  • Effect sizes statistically compatible with zero; strong potential for confounding (teacher differences, school policies, broader investment).
• This places the study low in evidence hierarchies; adequate to justify “interesting hypothesis,” not sweeping policy claims about “surprisingly large” gains.

Skepticism, Replication, and Policy

• Debate over HN’s culture: some emphasize the necessity of aggressively probing flaws (given publication bias and many false positives); others warn against reflexive dismissal and “lazy cynicism.”
• Several note that separate literatures already link air pollution to reduced cognitive performance in workers, students, and professionals, so the direction of effect is plausible even if the magnitude here is not.
• Some argue you don’t need outsized test-score gains to justify filtration: reduced illness, comfort, and parity with water/food standards for “clean air” may be sufficient.