The "accidental shootings" is negligible and has no real place in this discussion. When we're talking about people whose job it is to protect others, then for sure there are more lives saved by arming people than there are lives lost.

I don't know how you get to a net increase in deaths by arming teachers, forcing potential mass killers to go elsewhere for their killing spree.

And yes, reducing school shootings should certainly be a priority, like the first place to start when it comes to dealing with the problem.