if there's only 10 when they split them up, I don't think that's too bad at all. the class you're in now w/ 20 - oh my - that seems way too much for 1 instructor.
The school I use only allows 7 at the most, in any of their classes.
and you're absolutely right, it's either deal w/ the large class size and actually attend classes, or not at all... I'd take the risk w/ the large class and get the socializing and training. At the very least, you'll learn new techniques that you can practice at home - and at your own "puppy playdates". I take full advantage of my friend or family bbq parties - since most ppl I know have dogs, we bring them and practice training at our own social events.
let us know how the observation goes!
that this is the right class for you!