The FBO I went to was offering a night ground school course when I started my private, so I did that. Though I don't think I really learned much--or anything at all--that I wouldn't have picked up on my own. My instructor didn't do any ground with me except to prep for the solo, solo XC, and checkride to make sure I had a decent handle on things. He did, however, do something cool--once I got the hang of flying he would quiz me on everything up in the air--partly as a distraction to help me learn to multitask and think on my toes.
How much ground school you'll need to do with your instructor is a function of how diligent you are at studying on your own and how well you can understand and apply the book info in the cockpit.