Don't they have those 'alternative' learning schools here, which are basically where all the expelled kids have to go?
The council buses them from around town and the school looks like a fortress because, well, some of the pupils are convicted criminals.
My sister is a secondary school teacher in Texas and they actually have police at the school - that's their beat.
Difference is, they do have to exclude some pupils for good. Most of the time, it's pupil on pupil violence that causes this, as there are active gang members.
Some have even had to be incarcerated/serve custodial sentences (violent crimes committed off campus).
But the premise there is, well, a school is public property.
If you assault someone on a public footpath, you ge arrested. But here it seems, if it happens in school, it's covered up or the people aren't prosecuted.