He may well have gotten the idea from the man who killed the Amish girls. That's similar to what he did. These unstable perps feed off of the ideas of other unstable people.
I was wondering about that earlier myself. However, Amish schoolhouse vs. Virginia Tech. is a bit of a different dynamic.
With the former, you've got (many) fewer pupils, so managing the situation and controlling the people would be easier.
With the latter, you've got adults, who are physically much larger and stronger, and there's more of them.
That said, I'm surprised to hear students actually lined up (if that's really what happened). You'd think everyone would scramble and panic or try to escape.