I actually looked up the school and went to their website after realizing it was a Christian school.
I don't recommend following suit (it's Covenant School, it's a private religious school in Nashville).
Let's just say I suspect the truth is that they were bullied and abused there and that is why it was the target when they finally snapped. It's a very classic Evangelical school where boys are taught to be Real Men and girls are taught to be Helpmeets.
Obviously, I don't justify or excuse what they did at *all*. Shooting at kids is evil regardless of motivation.
But I think I may have an understanding of why they shot up the school not, say, their most recent place of employment.