Fire drills still happen with no warning to the children. At our school and every other school I’ve been at, the bell just rings in a certain way and the kids get up and leave. Over the last 10 years, we have had 4 genuine emergencies and the kids acted no differently than from a drill, because until they got outside and found out what really happened, they assumed it was a drill. Which is how it is supposed to happen - handle drills calmly in practice and when it is real, the drill goes calmly then also.
Putting students in a state of mortal dread, and hammering it home by having a disguised person pull on the doorknob, is nowhere near the same category as a fire drill.
Yes, and wouldn’t you want children to learn to react to a terrorist attack in the same calm manner as a fire drill. I use calm loosely here, because sometimes there’s an awful lot of giggling but that would be better than panic in the real thing.
I’m sure that not everything the teachers did was the optimal approach, but to assume in knee-jerk reaction that such drilling is inappropriate is simply wrong and ill-thought out.