I think my Dad had it right. He said, “You don’t need a gun very often. But when you need a gun, you really, really need a gun.”
If every teacher in America was armed, it is highly likely there would be a steady drumbeat of accidents and “workplace violence” incidents resulting in a steady injury and mortality rate.
That’s due just to the Law of Large Numbers. ~50M students and ~4M teachers, a not insignificant percentage of whom are not overy intelligent and some of whom are no doubt disturbed, means some of those 4M guns will be misused, accidentally or on purpose.
After all, cops accidentally shoot themselves with some frequency, and there aren’t 4M cops in America, only about 800K.
OTOH, the chance of a Newtown or Columbine type mass shooting would be very small.
I spent a couple of hours yesterday driving Highway 7 through north central Arkansas yesterday; it is a beautiful trip through the Ozark Mountains. If you really take a look at the folks that live along that route, you will know very quickly that they do NOT much approve of Obama or his ways. If the feds want to try to grab their guns, then the confiscators will learn a very harsh lesson in mountain law.
We already have twice that number of CCW holders in the country, and what you predict has not happened. The number of accidents is tiny. I recall about 4 in twenty years. Each one was highly publicized. None were fatal.
Fatal firearms accidents are very rare (about two per million of population), and most of those occur in the very small subset of irresponsible people who do very risky stuff without considering consequences.