High school on a military base in Europe. We had bomb threats and bomb threat practices as often as we did fire drills. Yeah, bomb threat practices. Fun thing too, was every time, because it could have been an actual threat, the MP's had to come in with bomb sniffing dogs to clear the place. Took a good hour each time.
The thing I don't get isn't doing a bomb threat. It's doing a bomb threat where the security guards are TRAINED PROFESSIONAL KILLERS. It's not a question of if you get caught, it's when, how, and what kind of beating they argue about giving you while you're hog-tied in a corner.
But in your situation, I gotta hand it to ya. I never had the kid call in in advance and give a window of a couple days. Personally I'd have to go with the power motive rather than homework, since it would give the kid the feeling of owning the school for those couple days.