[Douchetallica]

Extra precaution never hurts.
A mock attack is really the best way to do it, you catch people off guard and see how they would really react.
Whenever schools/work places have fire drills, they usually never tell you, you just proceed as if it were the real deal.

Did teachers have good intentions? Yes.
Did the teachers carry it out well with no one getting hurt? Yes.
Did the kids learn something from the mocked attack? Yes (or so I hope).
Did the teachers execute it out wrong? Perhaps.
Should anyone lose their jobs? No.

If the parents take it to court... eh, I guess they'd rather want their kids in coffins come the next real horrible tragedy. Teachers were just trying to help out, even if they did proceed it what some may deem "wrongfully".