So do they restrict entry into the school? Did the guy have to check in with anyone before entering? Lock downs might work if you can reasonably expect to keep the potential attacker out. If the attacker is already inside, I am not sure how well that works.
A lockdown means each teacher closes and locks the door to each classroom. Of course, the way most classroom doors are arranged and the way classroom locks work, this typically requires each teacher to step out into the corridor with the key in order to lock the door before pulling it closed. Tough assignment if the shooter is in your corridor ...
Newer schools are getting different hardware (including electronic locks that can all be secured by the push of a button in the main office -- unless, of course, the folks in the main office are already dead -- like at Sandy Hook), but there must be tens or hundreds of thousands of schools across the country with the old style locks, and no money to replace them.
