Lots of people get private training for their dogs, and of course that sounds great to me. But every dog needs a hobby in addition to having a trainer come in. Just because your dog knows sit and down doesn't mean he can't learn one hundred additional things. Every dog needs an obedience class at the very least. Every dog. No matter how good a trainer is; no matter how good his person is. Just because Duncan will sit in the kitchen to wait for dinner doesn't mean he'll do it in a new environment with other dogs and people around. That's how you get a dog who really listens.
If your puppy is still under six months, she should definitely be in a puppy class, and I don't mean at one of the popular pet store chains but rather with a truly qualified professional supervising bully puppies and keeping every situation positive. If your pup is older than seven months, he probably should go to a novice/beginner obedience class. Even if he is the most perfectly behaved dog, couldn't you use advice and a support group, anyway? And the most perfect dog needs class just as much.
You may think you don't have time for a weekly class, but it's usually just an hour for six or eight weeks. Imagine how bored your dog probably is without the stimulation of being in class. Because our dogs are with us on earth for much too short a time, we need to go out and squeeze out every bit of fun and give them the most interesting existence ever. They deserve that.
So who needs class? You do!
(Where to go? Ask me and I'll tell you!)