I don’t think anybody is adequately prepared for this kind of situation. This is why the “arm all the teachers!” argument is so absolutely asinine. Police on scene folded and could only do “crowd control”. Even the one off duty guy who ended up going in after an hour had to go around asking all the staff for a key to the room to get in, as they couldn’t “bust in”.
Had to unlock the door to go in and kill the guy, but by then, as far as I know, everybody inside the room was dead.