School Gun Shootings: Access to Guns or Something Else?

I don't think anyone will assert (if you do, please cite sources) that school gun shootings were more prevalent in the U.S. fifty, sixty or seventy years ago than today.

I also don't think that anyone can seriously argue that access to guns was more strictly controlled fifty, sixty or seventy years ago than today.

So, then, if access to guns was far easier fifty, sixty or seventy years ago than today and yet there were not just fewer but FAR FEWER school shootings than today, isn't it reasonable to conclude that other factors are at work that are resulting in FAR MORE school shootings than simply the mere access to a firearm?

EDIT:
Statistical reference
https://en.wikipedia.org/wiki/List_of_school_shootings_in_the_United_States

School Massacres Around the World
https://en.wikipedia.org/wiki/List_of_school_massacres_by_death_toll