Yeh, the irony that the NRA types, mostly small gov types railing about government largesse, are quite happy to arm government agents and insert them into their kids' schools. It's.....baffling.
Incidentally, worth pointing out that there was an armed bloke at Columbine who was shot at by Eric Harris so the scheme, absurd and easily rejected on its face, has a relevant precedent for how well it likely won't change much. Sure, the poor numpty with the gun might get lucky and stop a gunman but it's more likely he'll just be the first one to die.
The logistics alone for such an idea are staggering, really. Just to pick on one issue, training, let's assume that it won't be turned into a minimum wage-slave position (which it will). Who will make sure they're up to scratch with the range scores? If you make them pay it for themselves, how will you ensure it's adequate? Will the NRA be happy for yet another massive bureaucratic department to be formed to deal with this? The vast majority of coppers would never volunteer to be put in a position where the other guy has the element of surprise and is likely far more heavily armed, no amount of training can guarantee even a fighting chance in that situation so why would anyone expect said wage-slave to potentially sacrifice their lives for this **** detail?