I bought three wood bats from
MAXBAT last July and my son is still training with the bat he started with. All of them are 31" bats and weigh between 25-27 ounces (-5 to -7).
I agree with what you (SDBB & AgentDad) are saying about the heavier wood bats. However I think training with wood really depends on the kid. Obviously I wouldn't put a -3 into my 12 year olds hands, but the bat(s) we do use he's able to handle. I video a LOT so I know whether or not his mechanics are holding up. Swinging a wood bat can be more taxing on you than the lighter aluminum bats so you have to build up to them. Start slowly, maybe choke up a bit. If anything the heavier bats promote proper mechanics.
If you have proper swing mechanics your swing should hold up with wood. Of course if you use more of your arms to swing it probably won't hold up very well with wood. This is one of the problems with the lighter bats. They are so light they can get a player swinging with his arms more. At least that is what I've experienced with kids.
A good swing is a good swing whether you're using wood or aluminum. Whatever you feel you need to do to get that proper swing is what you should be doing during training. When it comes to games though I'd use what everyone else is using.
Good Luck!
Jason