@Kibble29 I'll just add here that I did a bit of supply early on this year.
I had a situation where a boy came running screaming into my class (after the bell - he wasn't one of mine) closely followed by a thug.
They were only S1/Y8. No panic button in this school and I couldn't get to the phone. Managed to walk the thug backwards out of the door and lock it. (Yes, I worried that I'd be in trouble for doing that. There's also the fact that I'm in my 60s with bad knees, bad shoulders and arthritis.) Phoned for back up.
in the meantime, one of the kids still in the room gleefully opened the door. (The lock only operates on the exterior, not the interior.) Of course, the bully ran back in.
I had to put the victim in the corner of the classroom and stand in front of him while we waited for assistance. If they'd been a bit older and bigger, I'd have had no chance.
I later found out that the victim had been assaulted by the thug previously and that the usual useless measures had been taken. As you say, the school might as well have put a neon light above the victim's head. The thug has a difficult home life, apparently.
I'm sympathetic to that, but my sympathy ends when he starts to beat another child.