The lady with the gun isn't a teacher. She is an aide of some sort - parent, volunteer.
We also don't know the circumstances of where the photo was taken. It may or may not be on school grounds.
But here is my first hand experience: when I visited Israel in the 1980's our tour group was at an outdoor historical place (Bet Shean, IIRC) and in attendance was a group of 20 or so middle school aged children. Nearby was a nice young fellow in civilian clothes with an M1 carbine. I engaged him in conversation and asked what was going on with the gun. He said (in a Bronx accent) "I'm a guard for these children's field trip."
My understanding is at the schools themselves they are fenced in and have guards of some sort (armed or otherwise). Individuals need to present ID.
I like the idea of what the photo presents, but we have to get our facts straight.
Someone pointed out that having the teachers armed may not be the best option, since they are in situations where accidents (kids are curious) could have bad results, but more so because they are not free to roam the buildings and appear at random (and, for an armed intruder, unpredictable) places.
Trained parents and volunteers, however, would be a great idea.
It doesn’t matter where the picture was taken. The ages of those young kids are all I need to know (although I appreciate the sense of your comment in that the leftists will jump on any perceived erroneous statement to prove how “dumb” we all are).