I think the key here is with out parental notification. I remember in the fifties when I was in school we had city wide disaster (they were actually nuclear) drills where we would practise evacuating everyone. These were the hot days of the cold war and we were very near a possible ground zero. It was almost as good as a snow day but not quite. Because everyone was involved parents knew a) their children would be sent to a particular location and b) they had to show up at a particular location as well. These didn’t happen all that often but they were a stark reminder of the risks involved in living.