Spree shootings aren't common, what's changed is how the media covers it. There have always been crazy people, and they have always done horrible things.
I think the biggest issue is parenting, as well as our approach to the mentally ill. I think doctors and parents today, are more willing to turn to drugs to help children instead of going with the more difficult route of actually working at behavioral therapy and hands on parenting.
I think the first student killing students in the US was back in the 1970's.
Why do you think that? What makes you believe that it never happened in...say, the 1800's?
I wasn't around back then, I can only speak about the last 60+ years. If you have something let me know.