When I worked for Gwinnett County Schools, I was the first called when doors were found open at my school. There were only 3 men in the school and I lived closest. The police officers wouldn't go inside until I got there and I always carried a gun. The way the classrooms were set up, you were a sitting duck in the hallways and going into the classrooms, which had no windows. The rooms were two deep between the hall and outside and only the outside classroom had a door with a window in the door. It may have been school policy for no guns and it was certainly State Gun Free Zone, but my principal never complained. He even knew I kept in my car in the parking lot. If I had ever been caught by an unknowing police officer, I would have pleaded that I forgot I had it in the car.
