I think this kind of question is a good place for that old proverb or saying: "don't smooth the path for your child, but prepare your child for the path" (loosely paraphrased, I'm sure, but it goes something like that).
Sam is getting good grades, you don't mention that he's received any punishments from this teacher such as detention, the teacher hasn't spoken to you regarding any negative behavior on Sam's part. So he's getting the education that he should be, and the only thing he seems to be suffering, from what you've written, is a personal disappointment in how the teacher appears to regard him, and a disappointment in the behavior of some of his classmates ("the kiss-ups" and the attention they receive).
That does not seem to merit a parent-teacher conference, nor should you just "leave it", which is one of your options that you listed.
This is the time and place to prepare Sam for the path ahead. Approval is nice, of course. Recognition is nice, of course. But it's not what we should strive for. Sam might be able to start learning that personal development, personal responsibility, integrity, and moral strength are what will carry him through the rocky areas of life. There will always be the attention-grabber, the person we can never seem to please no matter what, the person who dislikes us because of some vague unexplainable reason that makes no sense whatsoever.
Snide comments and jokes that aren't really funny will get more and more common as Sam grows older. Ask Sam if he's doing his best. Ask him if he's being a helpful classmate, a good friend, a respectful student. Ask him if there's anything he can personally improve on (does he roll his eyes and mutter something when one of the "kiss-ups" gets yet another gold star?). Talk with him about people who crave attention and who get ahead by doing anything to get into favor with the one in charge, vs people who have integrity and personal strength regardless of recognition. The one in charge may get reassigned, and what does the "kiss-up" have then? Nothing to stand on. But the one who maintains a good work ethic has a solid foundation.
I'm sorry Sam is discouraged by this teacher. Sadly he will encounter more people who act like that, and now is a great time to help Sam become a strong young man from the inside out.