The introductory scene of book five follows the same pattern as the introductory paragraphs of book one--the way that they're structured suggests that what we should be looking for is the way in which the interlocutors have changed since the first encounter. I brought this up in the last class, and was very happy with where the conversation went, but I don't think we actually explored it in depth before branching off.
So, have Glaucon/Adeimantus/Polemarchus/Thrasymachus changed since the first encounter? Or are the legal formulas/forceful language that they employ to goad Socrates still enforcing the same sporting attitude with which they began? Is the scene pessimistic or optimistic concerning Socrates' ability to educate the young Athenians? If they have changed, in what ways have they changed? If they haven't changed, what tactics might Socrates employ next to urge them on to their own conclusions?
I'll offer my own answer in the comments if they get off the ground.