Check out that wiki page of school shootings, nothing has changed since 1800's that's when school shootings started to increase. It seems that guns where easier to obtain starting around the 1800's and has increased over time.
I've never argued against it. Were guns nonexistent, the problem wouldn't disappear. If somebody wants to kill they are going to find a way to do it. The worst school massacre in history involved zero firearms. The argument doesn't involve guns. It involves people. The weapon of choice is irrelevant. It's the why it's happening that needs to be addressed.