While in general the attending has the final say on the grades the smart ones will listen to the residents on borderline cases. If you're clearly on one side or the other of the divide by either having excelled in the structured teaching sessions or made a total fool/ass of yourself the resident likely won't have much input, but if you're the average run of the mill student who does well most of the time at the teaching sessions, the resident's input on how well you function as a member of the team will shift you one way or another.
At least in an ideal world.