"Let's roll." That's so simple, but I think it might work. Two little words, that bring to mind the actions of the passengers of Flight 93. I think it just might make it clear to everyone, in a split second, what must be done.
That's pretty hard to tell a child. To run towards the danger instead of away from it? I have thought the same thing. But would you want that first child that is shot in the rush to gang takle the assailant to be yours? I am more in favor of arming the teachers. Or posting armed guards at the schools.