I went looking for a timeline to help me understand when school shootings started to be a thing. I found this -
http://www.infoplease.com/ipa/A0777958.html
Which only goes back to 1996 - but it is interesting.
Separating out one on one shootings - kid hates teacher - from kid suits up and goes in full commando style, I'd like to trace it back to its roots.