There is only one round of mixed meter conducting. Each conductor on a particular day will use the same piece. Meet with the others scheduled to conduct that day and together choose a piece and an alternate to present to Dr. Daugherty for approval. This joint planning needs to be done well in advance of your scheduled conducting day. Together with your team work out a rehearsal plan: (1) how much of the piece your team will do; (2) how you are going to sequence it to teach to the class; (3) what each conductor will teach/work on. Guideline: The piece (or the part of it you choose to teach) should change meter at least three times. At least one of those times, the bottom number of the time signature should change. In certain cases, 6/8 can constitute mixed meter (if the pulse alternates between 2 and 3). This guideline is not written in stone. That's why it's important to let Dr. Daugherty see/approve your piece beforehand. He just wants to make sure you don't choose something "too easy!" When searching in the choral library, you will pretty much limit your search to the twentieth and twenty-first century sections, though some Renaissance pieces may also work.