And in an emergency, you would have them do what - make 1000 phone calls to ask all the parents if it's OK to evac?
I think the solution is simple. The school should send a form home to every parent, asking a simple "yes" or "no" to the question, "In the event of an emergency, may we act
in loco parentis to protect the safety of your children?" The parents that check "yes" have their children hustled off to safety when some kid goes Columbine on the school. The parents that said "no" will have their kids sent out the front door to wait outside for the parents to come pick them up.
How's that?