I have the bad feeling that the kid that was stabbing them wasn't in a classroom nor were they in a spot adults could get to quickly or they were relatively skilled and gonzo, from the descriptions of the kind of wounds the victims suffered. It was not a simple bunch of slashings they were deep, nasty wounds. Maybe the kid was on drugs and freaked. Speculation is not all that good though.
Aha...just 15 minutes after the school open and he had two knives so classes weren't in session and a security guard ws also injured before he was tackled. Another smart, quiet, sorta friendly knifewielding sophomore.
Now it falls into place somehow.