Certainly an interesting idea. Profoundly stupid execution, and it will cause their lawyers headaches for the months and years to come. There will be immunity issues, but there will also be public opinion issues. Cases with great defenses sometimes settle because of public exposure alone.
It got me wondering though... When I was in school (in Kansas) we occasionally had tornado drills and routinely had fire drills. It's my understanding that during the height of the cold war nuclear drills were conducted. I know for a fact that more school children have been killed by gunmen than by nuclear attacks, and I suspect gunmen out number tornadoes as well.
Of course the counter to that argument is that more people are killed every year by peanut allergies and bee stings than by school shootings... but if you are going to drill for something, shouldn't it at least be the more likely danger?