Just to throw in my two cents, I have about 25 squads of 2 dwarves each. (I have a 100 dwarf fort where all males are drafted). I never put them in squads of 3, only 2 at a time. You have a two sparring partners for life (or death, whichever comes first) If you get two COMPLETELY untrained in any combat dwarves and squad them in pairs, they will start sparring off the bat (most of the time). Give them the same weapon (should go without saying), and the only time they will take a break is when one of them creeps ahead of the other and does a training session to get his partner caught up. I did bring two bronze swords with me on embark, that way I could draft the males right away. My embark ended up having no metal, and I didn't wanna go straight for the pink stuff, so my first two males both got the starting short swords, my second two got the starting axes, my third ones got some migrant axes, my fourth ones got large daggers or elfwood swords, ECT ECT ECT. By year two the traders were bringing real weapons, but I had several legendary weapon users. I'm still working on legendary scourge and whip users, since weapons are so scarce. They handled a large siege no prob, the only losses came from the first ambush, since the first ambush was quickly followed by a second ambush right next to the raw recruits.
Anyways, squads of two. It just works better. Now putting a legendary soldier as a teacher in a class of rookies MIGHT work great, but squads of two do the trick for me, just don't give them any time off unless they are seriously depressed.