Not to dis your idea, but having been around rent a cops, I'm not sure I'd trust the lives of children to them. Most places that hire them, hire only ONE. A well placed head shot would eliminate them whereas the nut jobs would have a more difficult time in taking out a school full of armed teachers. As soon as the school alarm is sounded, all teachers except for the one that is in the room with Mr. Whacko escort the children out of the building. That teacher engages the nut and keeps him occupied knowing that the other teachers are on their way back into the building to partake in some enjoyable target shooting.

Place the whacko's shot up body in front of the school with a sign: "This is how we deal with sickos". Leave the body in front of the school for a full week so that the media can get plenty of news coverage.