Before the GCA 1968, this kind of stuff did not happen...The worst school mass killing was in 1927,,,and it was by a BOMB not a shooting...I challange you to find a school shooting prior to the GCA1968? If you find one, tells us all about it OK?
That's a bit broad, I can think of one without even looking...Charles Whitman at the University of Texas 1966. I'd imagine there are others. "This kind of stuff", spree/mass killing, most certainly happened before 1968 and will continue to happen, regardless of the method used.