My dd secondary school had a policy that classrooms over 35 degrees were locked and the class was merged with another class or relocated to a cooler room (since over half the kids didn’t show up and Y11 and Y13 already left there was space).
Lunch was a problem so y7 and y8 were herded into the sports hall with “a million fans” to keep cool.
Dd walked home 40mins in the baking heat. I said she can skip tomorrow if it’s too much for her.