This discussion needs some clarity. First of all, I am a teacher. Second, I am strong supporter of the 2nd Amendment. Third, our school system has no business mandating that anyone should be forced to carry a gun when they are uncomfortable doing so. What I advocate, and armed teacher proponents advocate, is allowing the individual teacher to make that decision. Many teachers are veterans, avid hunters or sportsman, or gun enthusiasts who are very comfortable with guns. Many of them grew up around guns. They can be trusted with them and they can provide an added layer of on-site security that law enforcement cannot. They should not be denied the choice to carry a gun on the job.
The hysterical reactions to armed teachers has been deliberately misframed. No one, myself included, expects an armed teacher to engage in a shoot-out or track and find a gunman whose specific location on a school campus is not known. That is an offensive strategy best left to law enforcement professionals. I do not advocate teachers running around campus looking to engage in a shoot-out. I do, however, advocate teachers who are comfortable with firearms having a defensive strategy that protects the students in their classrooms.
Here is what I would do if being armed on my campus were allowed. If a campus alert went out, I would lock my door and put all of my students in a defensive position: away from the windows, under their desks, or behind barricades. As their teacher, I would take a defensive position behind a desk. My firearm would be at the ready, covering the access point to my classroom. If the gunman manages to get through a locked door and and poses a threat to my students, I would engage him at that time considering, of course, that my life is now in danger. Engaging a gunman in this scenario is self-defense. Consider how this scenarion would turn out if I was not armed?
I hear many teachers who are opposed to being armed say, "I'd die for my students." Without a strategy for self-defense? That may, indeed, be the result...and an unnecessary result. Or, "I don't want to shoot another student," while they are willing to let their students be shot as unprotected targets of a mass-shooter. I would prefer teachers say, "I want my students to live. I want to live. I don't want to shoot anyone but I will have a strategy which increases our chances of survival in school-shooting scenario." But let's let the teachers decide. For myself, as a teacher, I want to live. I want my students to live. And I don't want the "system" deciding the risks I should take with my life and the lives of my students.
Mishaps? Yes. There have been mishaps...mishaps, so far, which did not involve loss of life. A determined gunman shooting up a school, with no resistance or strategy to neutralize him, can produce a significant death toll. We've seen it. I'll take the chance of a mishap over the certainty of mass casualties. And mishaps can be eliminated with proper training. The worn out cliche, "Arm teachers with supplies/teaching time/ not guns" is a false and reckless comparison. You can fill every teacher's classroom with ample supplies, double their salaries, or anything else. It still doesn't serve as an effective defensive strategy against an armed threat to murder students.