is it a good idea?  probably not.  will there be an accidental shooting, or some other incident where a kid gets a gun away from the teacher, then goes nuclear?  almost certainly.  when it comes to our children’s safety, emotions always amp up to a fever pitch.  throw in a columbine et. al., and you have a certain sect that wants teachers to have guns. 
 
i grew up in a rural state, and recently moved back there, in the northwest.  guns were, and are, the norm.  hell, we ALL had guns in our trucks we drove to school in the late 70’s.  obviously, not anymore.
 
as far as pulling the trigger, i have only this too add- a few years ago i was working 3 12’s and bored on the four days off i had every week.  i took a job as security guard, transporting huge sums of money between banks.  we had sidearms and shotguns- and [b][i]one day[/i][/b] of training.  one day.   and, the statistics told us we had less than 1.8 seconds to make a decision about whether or not to pull the trigger.  this in an industry where you are a target, and anybody coming after you is fair game.  imagine an untrained teacher in a classroom when the shots ring out.  a recipe for disaster.