Yes.Would being surrounded by bullies 24-7 make someone snap?
Without looking into school shootings on a case-by-case basis, I would say shooting innocent people is indicative of some other motivation aside of revenge against bullying.
Speaking for myself, I was bullied relentlessly up until the point I got into a fight and suspended out of school.
I was an easy target because I was visibly queer, I was the ugly kid, and socially inept beyond redemption. I started carrying weapons to school, like crowbars, and I had fantasies for hours about breaking someones skull with it. I think if the right set of buttons were pushed, I would have. Even just thinking about it now makes me absolutely rage.
School shootings, no. Beating the ever living **** out of bullies, yes yes yes.