I know I'm certainly not the first one to have the idea, but I did have similar idea. I even posted about it on a thread where someone was asking for other ideas on what would you do if you were in a VT type situation...
http://thehighroad.org/showpost.php?p=3314131&postcount=34
Hmmm, if I had the resources... I see a morbid but possibly real opportunity, at least sales to the more affluent parent...
A Kevlar style backpack, possibly reinforced on one side (the flat side) w/ a plate of some type. Then, the zippers unzip all the way around and when you do this, additional material is let loose so you can slip it on as a vest (if you've ever seen any convertible/portable clothing that can be zipped up to be their own carry bag, or temp rain suit for golfers, you'll know what I mean) velcro straps to secure it around the body.
I admit it's kind of out there, but it could be done, so it doent' help the guy getting 'sucker shot' but if you hear gun fire you could drop your bag, unzip it and slip it on if you were in a place where you didn't have a free getaway (otherwise you would have already gotten away) while it wouldn't help at point blank range, it might help if you had to try a counter attack, or had a chance to get away but knew you might still get shot at in the process.
Just thinking out loud. As for practical things you'd already have at your disposal, I can't think of too many things that would help a sitting duck except to not be a sitting duck, move, run, or if your stuck somewhere barricade yourself in the room and/or have a plan to attack the gunman once he enters, grab a flagpole (do they still have those in class rooms?), break a chair leg off, a broom handle, find some glass that's not safety glass (if that's possible) and break it, tie it w/ some clothing around a stick, find a bottle of something flamable in a janitor's closet or lab, and throw a molitaf (spelling?) cocktail at him, find some other chemical and throw it in his eyes when he comes in the room, wet down the floor w/ soapy water and some how encourage him to run into it fall on his ass and jump him or hit him w/ one of the above, fire extinguisher to the face, or if strong enough hit him over the head w/ it as he enters the room, i don't know, still thinking out loud...
Basically think "home alone" w/ higher stakes, since it's not a movie you're in.
Karz
So, I was thinking a little further down the road w/ it, like not just make a backpack that has some bullet resistance, but actually make it convertible to be more effective to protect front, not just on your back, and have an option to slip a plate in it for more protection. Again, not for the sitting duck as much as for someone trying to do something, defend, get away, might provide some protection, or at least help get the nerve up to try something smart, like defend or flee...
I don't know what these guys' product looks like, but I think you could make something like this be cool, and not everyone has to know what it is, just don't put a 5.11 tactical tag on it.
I don't fault these guys for trying this, hey if there's a market for it, go for it. It's just like a dude on Rush the other week, he sells something w/ his company that helps other companies save big money on their power bills, paying for their equipment many times over. He was stuggling w/ the idea that he doesn't want to play on people's fear that their product will stop global warming, and wants to sell based on the cost savings to the companies, because he doesn't agree politically or scientifically with global warming. But the reality is, he doesn't have to be over the top about it, but if someone wants to buy it for environmental reasons or fiscal reasons, I say let em buy it, if it's a good thing, and they see value in it.
Same w/ this, if people want it, let em buy it. I don't encourage them to play on people's fears out of proportion, and would encourage to fight for more rights to self defense in these 'safe zones' but in the mean time, I see this as another layer of survival security.
Hey, if I hear shooting down the hall of any building, even if I was armed, but especially if I wasn't, and I had something nearby that had bullet resistant qualities, I'm gonna grab it, and then do whatever I need to do, wouldn't you?
Karz
my math teacher decided to weigh it one day for a problem and it was 58lbs 
