> I think this sort of violence is limited to a small fraction of schools/districts.

No, definitely not. I went to a decently-well-ranked suburban school district, and still witnessed violent incidents... no weapon used, but still multiple cases where the victim got a concussion. And there were arrests, a gun found in a kid's locker, etc. This stuff was unfortunately relatively normal, at least in the 90s. Not quite as often as at the school in the article, but still.