God bless plan A, but you know what they say about plans and contact with the enemy.
Now truthfully, not having any idea what the engagement will look like, other than you're the only unknown adult in a sea of kids, do you think your chances of neutralizing an unknown target are better with a concealed pistol, or a rifle?
In a perfect world always a rifle ....... but as a peacetime personal security detail aka kindergarten kop ....low profile I’d rather have a Sig 226 of 147gr frangables and a Glock 43 ankle rig backup.
I can “safely” fire down the hallway ceiling to disorient and confuse the active shooter and hopefully he isn’t a vet with a couple of tours as a door kicker and used to fright’n flight urges. Cropdusting the hallway per se.
Yes, getting to be an old man, lots of sudden stops, dressed casual, seasoned citizen who’s carry gear does not print. I’d love to be on a high vantage point with a precision long range rifle and kneecap anyone walking from the parking lot with anything bigger that a violin case (my SBR PDW).... to old to believe the racket ball carry case. Stop the threat before the even get to the door.
Add a few random places where you can see many approaches, “L” shaped intersecting halls, mirrors, security cameras only add to “mitigating” a slaughter.
Bring the fight fast and loud .....distract , disorient , confuse, scare the active shooter. Hell even put custom surround sound speakers playing machineguns and shotguns firing with sirens as the “lockdown” warning .......
Its not perfect .....just part of a layered defense in depth with a very fast response time.
Understand your valid concerns ....