One of the other things that bother me is where was the lock on these classrooms where he did the killing? Where was the alarm system?

One teacher should be able to trigger the locks in all the classrooms. It is probably time that all classrooms be equipped with an escape window.

At the very least give teachers flash bangs to toss in the hall before locking the door. I would also give the SRO K9's to turn loose on the shooter to distract them long enough to shoot them. A trained K9 will not cower in fear behind a pillar.