Ask yourself one simple question.
"If you were a mass murderer, would you go to a gun range to commit your mass murder?"
That can be answered with a unanimous no. Why is that? Because they shoot back. Simple.
The President and other political leaders all have armed guards. Why is that? So that they can shoot back. Simple.
Schools are gun free zones. Why is that? Not as simple. It is to protect the students from gun violence but, as the recent shootings have shown, that does not work. Why is that? There is no one to shoot back in a gun free zone.
A deranged individual set on massacring innocents, unless stopped, will.
A sane individual, will not.
If every teacher had a simple .357 snub nose revolver that they were required to carry. They could shoot back.