Even if a teacher had a gun, how effective would it be? The student just has to take the teacher out first. Plus, all civilians are trained to shoot guns in calm, collected manners. How many Joe shmoes are taught how to fire when they have adrenaline and fear surging through every part of their body? I imagine having a gun toting psychopath in your room would murder any demeanor and aiming skills you had. What if the teacher misses, and gets killed? Psych-Jack now just has more ammo.
Campus security is the biggest factor. I go to school on a campus of roughly 30,000, and I honestly never see any security. No one with tasers, hell, mace even. Nothing to at least hinder and slow down someone with a gun. A good starting point would be security per building. Two people, and always moving. Something happens in a building, they could simply press a button and get police/swat there ASAP. In the mean time, security has to do what they signed to do, put their life on the line.
Gun control has nothing to do with protecting students. Security needs to protect, and local police and swat need to have plans for any given building, schedule of classes, whatever.
I don't feel in danger while on campus, but I would like knowing if someone was packing heat, I would not have to rely on hiding alone.