Here are the problems with this drill: No one stated that this was a drill. Elementary students actually thought there was a man with a gun in their school. Sure, the thought was a good one... let's see how these students react so that we can analyze their mistakes and teach them the right way. However, I'd be really pissed off if my little girl came home scared out of her mind. There is probably no shortage of nightmares and traumatized children in this little town.
Good though... poor execution.