The problem isn't what you think, I'm sure on campus student's aren't allowed guns, so they're all unarmed, and unable to defend themselves.
The bad guy's can always get guns, even if they're banned. Just think of Dunblane, and this one in Germany
http://news.bbc.co.uk/2/hi/europe/1952869.stm
In both countries guns are banned, but it still happened. The problem is the students are unarmed, if they had guns these people would be dead before they could take a second life, or even a first one if lucky.
(As for the primary schools, of course 6 year old kids shouldn't be armed, but they're teachers should be.)