My 10 month old pup has never been to any classes. He's only played with a couple of my friends dogs. I can walk him off leash around the neighborhood and he ignores all dogs. Even ones tied up in the yard barking it's head off. Of course he looks but he doesn't care. I can train him in the front yard with the dog watching across the street and a little pomeranian barking behind a glass door. I want my dog to see and experience dogs big and small but I don't want him playing with them. I want him playing with me. I'm fun. They are not so there is no reason for him to want to run up to them.
If you have time and money of course take training classes. It definitely can't hurt but the reason your dog will be obedient is all the time spent training outside of class. Your dog isn't going to learn much during that one hour. That hour is there to teach you how to, it's on you to go home and do.