While I was thrilled when DF2014 came out in July, I've avoided getting sucked into Adventure mode much until a few of the bigger bug were squashed. With the "everyone runs away" problem taken care of in 0.40.10, I finally decided to get back into it.
It wasn't until then that I realized that the "Parry" option can be used to train weapon skills. (Yes, I skill grind.) This is a big deal, and I'm probably going to restart to take advantage of that fact sooner in my character's career. (Also, to add steelmaking to the humans.) However, I noticed that doing this also has the effect of training the weapons skills of whoever you're fighting - parry enough and eventually the bandit pikeman you're fighting will turn into a "pikemaster."
This brings me to my question: Is there a way to exploit this effect for companion training? If you can get someone to yield, will they eventually be amenable to joining you? Can you get companions from a civilization you're friendly with, take them out in the woods, provoke them to fight you, then yield/demand a yield without making the parent civ hostile? My current understanding is that the civilization won't know unless you or the companion tells someone about the attack, but rumor spreading and aggression are bugged so I'm not sure.
Of course, there's really no reason why you shouldn't be able to initiate a "training" fight with a companion, but as far as I know you can't do that yet.