Why not have some type of specialty for teachers that identify and qualify them to be on a team that reacts to active shooters in a school as well as other threats not yet identified.
We usually call the people we assign the responsibility of protecting us from criminals "police" or "security" officers. If the argument were that more of them should be hired, that'd be one thing. The idea of arming teachers to solve the school shooting problem sounds fine as a "why not" proposition. But, there are loads of questions.
For example, let's suppose that any public school teacher has the time to become certified to use a firearm. Let's say that all these communities have the funds to pay for the training.
Then, let's say that a student with an AR-15 begins to shoot up the school. He'd have to start somewhere, and unless the teacher in the first classroom had immediate access to a firearm with similar capacities, he'd be taken out relatively quickly. I mean. Nobody knows there's shooting until the shooting starts.
But, ok, let's say that the shooter picks a classroom where the teacher is not armed. It gets interesting. Does the armed teacher in another classroom have the obligation to leave his students and confront the suspect? If SHE doesn't, will she be held responsible for any deaths? That's either legally or just emotionally. The 4 armed officers who didn't enter the FL high school will probably be fired, but they're paid to risk their lives. If a teacher has that responsibility, the "pay incentive" should be a police officer's salary [edit] in addition to her teacher's pay.
However, suppose we have several classrooms with teachers armed with ARs themselves. What happens when a few of them come out into the hallways? If, God forbid, a teacher shoots another teacher or a student, who's responsible?
Now, if you asked me whether I thought it was ok for a teacher who is certified to carry to do so on school grounds, I'd say it depends totally on the state and the administrators of the particular school. Forcing teachers to carry or be around people who carry --which increases the likelihood of accidents-- is an infringement on their right not to be put in danger.