It’s incredibly unsafe when you live in a society built around smartphones/tablets for health and safety tools to remove said smartphones.
But is it? Landlines can make the same emergency calls. A Faraday cage also doesn’t mean you can’t have an internal wifi that reaches outside that the staff can connect to, or even the students can connect through with a proxy controlling their connection.
I agree it’s impractical. But it doesn’t mean laptops and phones suddenly don’t work. They can still work within the cage and you can poke holes through it with a landline and a proxy to control traffic in and out.
Ultimately, it’s definitely not worth the engineering and the effort. I just don’t think that safety is the reason it is impractical.