EDIT: I have come up with a second proposal as my initial one seems to be very flawed. Please scroll down to read it.
New Idea: One trained security person in each school with bullet proof vest. Possibly a veteran as they have trouble finding jobs and their war experience could give them an edge over the less experienced shooter. Laser point sight on the gun for maximum accuracy, but I don't know exactly what gun would be best for the situation; defiantly not an automatic though as less bullets in the air would be ideal.
Can you help me develop/refine this idea please?