Some of us have actually been in real situations and know personally wtf we're talking about. You apparently just play video-games.
You have concealed carried in schools and engaged bad guys in close combat?
You have been in a crowd of civilians and got into a firefight with a few badguys?
Do tell....
Now the very idea of a concealed carry teacher staying a secret past the first day is absurd. The idea of ALL the kids and most the parents NOT knowing who that teacher is after the first week is absurd.
Schools are HUGE, one pistol somewhere in it is like a needle in a hay stack.
Those of us who know WTF we are doing know it takes far more than one pistol in a school to have a good chance of stopping an active shooter before he either decides to stop or has a stoppage (jam to the amateurs) he can't reduce.
What someone who has experience in going up against someone actively shooting wants-
Numbers
Tactical advantage
Surprise
One teacher with a pistol isn't an advantage in numbers
Having to engage in a hallway is the equiv of a frontal assault, no tactical advantage, no fire and maneuver, no turn a flank
Since damn near every and any one connected to the school knows who the packing teacher is he can't count on the element of surprise.
So the single carry teacher has the deck stacked against him before he gets any opportunity to engage,and will engage under several severe disadvantages.
I'm far more inclined to make the ability of a shooter to gain access to a school far harder than now as opposed to putting a pistol packing teacher in a school.
I'm far more inclined to believe the best an armed teacher could do, if not targeted by the shooter right off the bat, is be a firewall. The shooter gets his way up until he runs into the teacher semi barricaded in a doorway and blocks further movement into the school.
But I'd say the first victim in such a school will be that teacher. Save lives? Possible, but so would making the job of an unauthorized entry far more difficult than it is.
Grunts know, once the bad guy(s) breech the perimeter all hell breaks loose.