Seriously, this is where liberalism turns nutty. I would ask my fellow liberals to look at the larger picture.
I concede that such training is possibly (if not likely) to have some bad consequences down the road. The kid who gets picked on in 3rd period by Jeff or Jill, will have access to a firearm in 6th period where Jeff or Jill may be in the same class. I further concede that with our cartoonish society and the volumes of mis-information on the web about the consequences of serious actions are characterized as everything from nominal to downright cool, it's probably not the gold of ideas to bring weapons into the schools with a seal of approval from the administration.
All that is conceded. What wins the day however are the facts that we live in a dangerous society so learning about the weapons that contribute to that danger is identical to girls learning about barrier contraception. Its really a matter of self defense. On the same theme as self defense, purchasing a gun and not knowing the first thing on how to use/maintain it maybe more dangerous in some cases for the owner than an intruder breaking into their residence. So why not? Thirdly, when your choices are other topics such as Clothing and Textiles, Pottery, or Football, there is some currency to learning real-world lessons; harsh though they may be.
I can think of a lot of things that I'd rather have taught in school but this isn't a loser of an idea out of the gate. Execution is, as always, the most important thing.