Contrary to popular thought teachers, being reasonable people, will not draw down on a problem maker and shoot him dead. Normal people will give some warning and be shot themselves
Having teachers with guns will elevate every school incident to a shoot or be shot event so the intruder will always come armed
SWAT teams are likely to shoot anyone with a gun first and find out of it was a teacher second
Teachers would have to have gun training and maintenance skills so they don't become a danger to themselves
Guns , ammo and training are an expense that school boards would have to cover. With 6.2 million teachers in the US at $1000 to arm and train them this is close to 10 billion dollars.
Collateral damage would see more students shot then bad guys. Depending on the rounds used a missed shot could be deadly after several walls were penetrated
Teachers flip out too (see videos of teachers hitting kids for examples) these same teachers would potentially shoot troublesome students. But then if the students were armed as well it could become really interesting.
