I suspect the only time the children would see the firearm, is when they have already heard gun shots down the hall, and the bangs are getting closer....I think at that point it's okay for the children to see their teacher grab a gun and likely save all their lives, and I nor any of the children or their parents would be too worried about the trauma caused by "seeing a gun". And what does availability have to do with anything? I don't understand the thought process that if there is a gun in school for security purposes, that means a student will have access to it too. I mean, there is a computer in the school that is capable of changing students grades, there is a safe somewhere with a bunch of cash from a previous bake sale, and there are knives in the cafeteria. Those would all by MUCH easier to access than the theoretical gun that is locked up and supervised at all times.
This idea is why we wouldn't have to pay for security personal, hence, making a gun accessible in case of emergency for 1 or 2 of the most qualified teachers. Guns don't cost that much, and even if they did, I'm not so sure we would worry about the cost when it comes to preventing a massacre of children. I believe if we were to do this, many people would volunteer their own guns, or the community might voluntarily pitch in 1$ each.
Building police stations into schools? I'm sure it would work, but it would probably also cost over a trillion dollars. Not to mention all the other functions of a police department, which might have strung out drug users or prostitutes being released/brought into the police station/school at any given time of the day.
"I want you to remember that, to remind you to stay out of my way. In all the years to come, in all your most private moments, I want you to remember my hand at your throat. I want you to remember the one man who beat you."