I just downloaded and installed the Peer Review DLC as well as a game update for Portal 2 on PS3. How do I actually play the new co-op mode, though? When I select co-op, all it lets me choose is Co-Op Standard or Co-Op Challenge, and in both cases the only levels I have access to are the original testing courses.
You or your partner must already have finished the regular co-op campaign.
Once you have, another pillar will appear in the hub which you can portal into. It will have two buttons, if both of you stand on one, you will be sucked into the new DLC.