Very few, I'm afraid. Teachers are (by and large) raving, antigun liberals. They'd sooner handle a live rattlesnake than a loaded gun. The benefit that would accrue is to folks in the extreme minority of Education (like me) who do in fact have the wherewithal, training and experience to make a difference in case the unthinkable becomes awful reality. But, that's all.
Unfortunately, you're probably right about the extent that it would help.
But to turn the antis' statement on its ear: If it saves one child...