Since I'm a teacher I'll throw my two cents in.
I have my permit, but even if I could carry at school I'm not sure I would and the reason why has to do with how police react in an active shooting situation.
We had a training 2 years ago with the local police about what to do in the event of a shooting. We were told that even if we get the chance to pick up a gun in a shooting situation not to, because when the police show up they will kill anyone who has a gun.
Given that piece of knowledge I'm not sure I'd want to have a gun in an active shooting situation.
Besides I teach science and I have gallons of hydrochloric acid in my classroom. My kids know that in the event of an active shooter, we lock the doors and fill beakers with acid. If the door opens, the person who opens it will get a beaker full of HCL in their face. I don't care how much body armor you wear, the HCL will find some expose spot and BURN LIKE HELL.