It doesn't always have to be live fire, it can be paint-ball for all I care, just something more than range target practice that accurately simulates an active shooter threat. But for the sake of argument, my friend was in the army from 2008-2013 and he said he was in at least 3 live fire exercises during the first year and a half, but he got real combat experience during his deployment in Iraq, so however you slice it, it's more than just concealed carry permit training. (1)
Yes, I'm aware LEO standards are all over the place, due to the fact that some officers work in districts with a budget, and some work in offices with like 1 sheriff and 4 deputies total. If the teachers pass a strict vetting process and have a steady diet of quality training, then I'd be okay with them having a gun that was securely stored away in their classroom, except for the fact that its going to eat away from budgets that are already painfully lean, let alone what happens when a teacher packing heat makes some kind of mistake and the district is sued for millions of dollars.