The easy fix is in front of everyone if they would look. Remove the restrictions keeping the school staff from being able to protect themselves and the children.
If the school principal had been armed with any reasonable firearm, she probably would not be dead, and how many other would also be alive, She tried to tackle the guy and got shot in the attempt.
Then I propose another idea, If this CT shoot had know that he COULD meet armed resistance...would he ahve even tried? Remember, as soon as LE showed up he committed suicide>>>?