While a vpn is never a bad thing, no you don’t need a vpn if you are watching debrid sources. Your ISP will see you connect to your debrid but it won’t see the vídeos you’re watching or anything like that. All Debrid (At least Real Debrid, the service many use) sources are encrypted and wont be picked up.
As a teacher, I will say that my administration is constantly telling us to limit the number of kids in the hall, especially during the last period of the day. I let my kids go pretty much whenever but I do try to follow a two person in the hall rule. Some people absolutely abuse the right to go to the bathroom and wander the entire period or whatever. It’s usually pretty easy to discern who needs to actually use the bathroom and I tend to take it easy on them but I have rules to follow too. I really would prefer to just let my kids go and I dont care that much about if they talk a bit with friends but they can be so irresponsible and just leave for 40 mins, or go smoke weed in the bathroom (it’s really common in my school) or whatever.