I'm operating off of memory, which isn't working so good lately, but I did Google up at least one. Oddly enough, it's in an article about arming teachers from last year.

http://www.msnbc.msn.com/id/7297575/

Froman cited the 1997 school shooting incident in Pearl, Miss., where a teacher retrieved a gun from his car when a student opened fire, then held the student at bay until police arrived.