By Greg Howard

Criteria. The best air filter for your elementary school classroom depends a lot on how friendly/hostile the teacher or school district is and how worried you are their being receptive to “non-mainstream” filters without a molded plastic shell. Safety and durability are also concerns, especially for units without fan guards and knowing that little kids like to stick fingers and objects where they don't belong.

Considering clean air delivery rate. Unfortunately, the manufacturer data on noise and clean air delivery rate ("CADR") is extremely inconsistent in its reliability, so while looking at the recommended room size is better than nothing when trying to maximize CADR, it's often not enough to have confidence in the "cleaning power" of the filter. Likewise, being a HEPA filter is less important than CADR. The more "DIY" units that use furnace filters can be a better choice for some, just like Corsi-Rosenthal boxes are solid.

Electronic cleaning. I wouldn't choose any filter with electronic cleaning that's not on the CARB list (certified to minimal ozone emission), but I also wouldn't turn on electronic cleaning features in a classroom. No UV, ionization, any of that. Stick to “fan and filter” cleaning, as electronic cleaning of all types can produce harmful byproducts besides ozone that build up in the absence of ventilation.

Recommendation. I landed on the Medify MA-125 for my kid's classroom because it can be scheduled (and its runtime monitored) from the power outlet using a Govee smart plug (even without Wi-Fi access), offers lots of speed choices to fine-tune the power/noise tradeoffs, draws in air from four sides, and vents at a 45-degree up-and-out angle that promotes room mixing. The downsides are that it has a UV feature (should never be turned on, but turns itself off after 30 minutes even if it’s activated accidentally) and it lacks a child-lock feature—so I have something Velcro'd to the control panel to (hopefully) discourage tampering.

Alternatives. Others have had luck with the AirFanta 3Pro and the Clean Air Kits Luggable or Brisk Box (cheaper options), but I'm hesitant to put unprotected PC fans in a room with young kids. You have more "big brand " choices if you're OK running the filter 24/7 (at the expense of filter life and the risk that someone will worry about power usage and shut it off), or if you can get Wi-Fi access to schedule on/off that way. If you need to schedule on/off without Wi-Fi access, the list of filter options shrinks considerably to the smaller (or more "DIY") brands plus the Medify MA-125, Coway Airmega 400, and the expensive Smart Air Blast and Blast Mini units. (Smart Air units discharge to the side, which I worry could be a nuisance for both room mixing and positioning.)

Good luck finding the right fit for your classroom!