I keep hearing hype about the bulletproof backpacks a couple of fathers created (though I had seen bulletproof backpacks and briefcases offered before these guys created theirs). The big selling point, as far as I have seen, is that they will stop "a variety of bullets, including 9mm hollowpoint bullets." This isn't that big a feat. A backpack full of books has a fairly good chance of stopping a 9mm hollowpoint.
I've also heard some people impressed because it stopped Uzi fire...which, oddly enough, is likely 9mm hollowpoints. If you want to hype it, you could say that it will stop most popular handgun calibers. Of course, that could be a lie, especially if we include FMJ bullets in the mix. I don't know what these packs are capable of, so I can't say for sure.
The question, though, is whether these $175 book bags are a sound investment. You say you'll pay anything to keep your kid alive, but the threat of a shooting is a small one. And, if there is a shooting, the backpack is only good if the kid can get it between the gun and his/her body before getting shot...and keep it that way until the police are able to neutralize the threat.
A more useful investment might be to train and arm teachers. If an armed teacher takes out the shooter, more lives can be saved than cowering behind a few bulletproof backpacks would save. On the radio today, the DJ actually said "so the kid would grab the backpack...and just kind of cower behind it, but it might save his life." The choice of words was probably unintentional, but it tells a lot about the current status of society. We train kids to cower and hope for the best.
When I was in school, there would've been a few trying to hide and avoid getting shot...but I really believe we would've had several charging the shooter (probably with pocketknives, pencils, and anything else we could grab). But it was small town. Hell, somebody probably would've gone to the parking lot and grabbed a rifle if it happened in hunting season, because there were rifles in students' cars then. Yeah, it was illegal, but no one cared at the time.
I'm not saying that we should tell kids to charge gunmen without regard for their own safety...but we should instill in them a value of survival that doesn't rely on the shooter not having enough time to shoot them. Maybe they would also take that sort of attitude into the rest of their lives, and fight for anything worth fighting for.
As for the backpacks, I just can't see spending $175 on a bag, even if it has kevlar inserts.