Prevention would be best, teaching faculty members ways to delay some wackjob would be the next step. Ever been in an enclosed area with a discharged fire extinguisher? You cant breath, fog them with it. Door jambs and get the kids out the windows and running away from the guy with the gun. School have an archery unit? Well arrows were dropping bad guys long before guns were. Scissors? They look like 2 knives pinned together to me.

Bad thing is, time is on the bad guys side.