I'm pretty certain that people haven't wanted their kids to look at porn for, well, nearly ever. So this isn't something "new" being invented, it's something very, very old being reformulated to recognize a new delivery technology.
You DID read that the OP said he was at a boarding school, right?
That means that the school's responsibility doesn't start when they get off the bus in the morning, and stop when they get on the bus to go home. This means that the kids are functionally wards of the school...meaning the school is responsible for them 24/7....ie, what they do in their spare time.
Considering that any possible harm that comes to the child - be it physical, emotional, psychological - ends up being the schools financial liability, then they are entirely within their remit to lock-down any computer systems used on their grounds. Don't like it? Don't browse the internet at their school.