Hey Shonna! I just read your blog about this and I feel the same way about the situation that you do. I'm sorry, but if they can call to tell me that my child has been absent from school (so that I'm aware just incase they were skipping school) and about the events that are taking place, then they should be able to tell me about a threat. So far I've been lucky that nothing like that has happened at my son's school (his middle school is next to the elementary school), but if it were to happen I'd certainly want to know.
We got called at the end of this last school year about a boy dying tragically and telling us that school counslors would be there to help the kids through it, so if they can do that then there is no excuse what so ever for them not to be able to inform you (or anyone for that matter) about something like this.