Couple of problems with this plan. First off the AR15's will be in a safe that only the Officer has access to so, how long will it take them to get the weapon operational?
My guess would be after alot of innocents had already been killed or how about if the Police Officer is killed then what good is the weapon?
Secondly has the Fontana School Board ever heard the term collateral damage? Can you imagine a shooter armed to the teeth with automatic weapons and quite possibly body armour shooting it out inside a school full of kids with a cop armed with another automatic weapon? The thought should terrify any sane person.
The only way these weapons are going to be a benefit to these schools is if they come under attack from an outside agency and have to be defended like the Alamo which unless North Korea declares war on the Fontana School board is highly unlikely.