My idea is to have gun in a locked compartment right next to every fire alarm. Have one sound for a fire alarm, one for storms and one for cooks with guns. When the trained teachers, trained janitors and maybe even trained students here gun shots they run to the nearest station, unlock the gun and go kill the bastard.
You could even tie the safes together electronically, so if one was opened, the special “prep with a gun” alarm would sound.