When I was in school every single classroom was wired for landlines and Ethernet. You can also set up your wifi networks in ways that limit certain things and not others.
Alright, but they're not wired now. Neither are bathrooms, cafeterias, hallways, or other place where someone might have a stroke, a heart attack, a seizure. And unfortunately, gunmen in school are a thing, and if you're a teacher, scrambling for the wall-phone while you can hear gunshots in the next room over is significantly more difficult than reaching into your pocket for your phone.
If phones in schools really are bad for kids, it seems like we could probably sort out some of these objections?