Schools in the US have officers specifically assigned to the school. Like the officer’s full time job is to patrol the halls. They’re called School Resource Officers, and they are a large part of the prison pipeline, as their entire job is focused on getting kids into the prison system. Kids get arrested for things that could be (and previously were) handled by school discipline instead. But since school admins don’t want to deal with it, (because it would require actually making decisions on a case-by-case basis), it’s easier for them to just default to having a kid carted off to juvie by the SRO.