My how things have changed since the sixties when I was in elementary school. We used to have "Duck and Cover" Drills, which is get under your desk and turn away from the windows for when the USSR would use atomic weapons. In Middle School, the only violence was when there would be a fist fight between classes or after school. In High School, excitement one time was when some guy took Karate Lessons after watching "Kung Fu", and beat the crap out of someone.
The last thing we worried about was some idiot walking in the door with a gun and using it. I don't even think the "Rent-a cop" security officer wore one. The first gun I ever owned was a .30 M1 Carbine my dad got me for Christmas. I did a History Project on "The Battle of the Bulge" when I was about twelve. I took the firing pin out of the rifle and put a thirty round banana clip in it and used it in my display. It was no big deal back then, told the bus driver and teacher the day before, and walked in the front door at school the next day with an assault rife slung on my shoulder. Now you can't bring a butter knife to school to help serve refreshments.
No, sitting under the desk waiting for some insane person to shoot you is not a good plan. Maybe if certain teachers carried concealed weapons and everybody was taught to run out the door at once or attack the assailant in mass is a better idea. Odds are that more people would survive. The story about the Amish Schoolgirls was horrible. The most amazing part was the attitude of the parents, who understood what Jesus actually taught. If most people understood what Love and Forgiveness is and lived like that, the world today would be a much better place.