When I was at Caltech there was an informal weekly thing where students in the freshman physics class who wanted some help or wanted to discuss some things from class in more depth could go as a group and get help from or discuss things with Richard Feynman. (One of my regrets is that I did reasonably well in freshman physics and was not smart enough to realize that spending time chatting about physics with Feynman would have been worthwhile even if I did not need it to pass the class).