From testimony given in March by David Helsel, the superintendent of the Blue Mountain School District, in Pennsylvania, at a meeting of the Pennsylvania House of Representatives education committee:From the October issue of Harper's. There's a bit more at the link, and it has a better title ("Schoolhouse Rocks").
Our district has been training staff and students in an armed-intruder defense plan. Every classroom has been equipped with a five-gallon bucket full of river stone. If an armed intruder attempts to gain entrance, they will face a classroom full of students armed with rocks. And they will be stoned...
Obviously the teachers have pepper spray. The rocks are just for students. We used to have them huddle underneath desks. We’ve learned from Virginia Tech: the gentleman that did it went to a shooting range a week before and put the targets on the ground because he knew students were going to be under the desks...