Many of the school-shooting persons are wearing body armor now.
If you have a gun and the school shooter doesnt go down aim below the belt. A leg shot will bring down almost anyone. Once down brain him.
What finally brought down the North Hollywood bank robbers equipped with AK 47s and body armor were leg shots from under cars they were hiding behind. One was killed by cops the other self inflicted after having his legs shot out from under him.
On the chance the Perp has groin "armor" if one goes to the side a bit there is a chance of hitting the femoral artery or at least the femur or pelvis/hip.
Even if body armor is hit the human body is going to pay close attention to the impact force.
U.S. Soldier hit by Baghdad sniper. Soldier had Hard Chest Plate Insert.