Portal 2 courses during Cooperative Testing Initiative
Course One: Team Building
This is one of the first courses available to the player upon entering the Hub, the others remaining locked until the other courses are completed. In this course, the players are given basic tests that emphasize the use of teamwork through portals and pinging, which is a function that allows players to communicate even without text or even through voice. Pings come in a variety of forms, from a simple "Look" ping, to a "Timer" ping that can be used to coordinate timed events effectively.
Course Two: Mass and Velocity
After completing Course One, this course will unlock for players to continue testing. This chamber utilizes the effects portals have when an object has both mass and velocity as it enters the portal, meaning the players must utilize both in order to pass this course.
Course Three: Hard-Light Surfaces
This course opens up upon completion of Course Two. In this course, the players must make use of the Light Bridges to both navigate chambers and act as a wall for other chambers as a defense mechanism or a creative way of stopping something from hurtling into acid. This course takes place in the Decayed/ruined look/style from the first 4 chapters in the singleplayer.
Course Four: Excursion Funnels
This course unlocks upon completion of Course Three. During this course, the player will have to make use of both Light Bridges and Excursion Funnels in order to complete these chambers. It will employ elements from the previous courses as well, making it much more difficult as the players progress. Apparentely this courses were made by GLaDOS for the bots themselves since she thought they weren't going to make it that far and just used tests for humans.
Course Five: Mobility Gels
This is the final course that unlocks after the completion of Course Four. Upon entering, GLaDOS will chime in and explain the significance of Atlas and P-Body's testing and what their true purpose is. The players are then dropped into the defunct Aperture testing spheres encountered during single player, and must make use of all elements from the previous chambers along with the Gels that are found in the course. The final course is very difficult, requiring both players to act as a true team. The last chamber is halted by a large vault door, which holds the frozen humans inside. Both players must perform any gesture to ultimately unlock the door. This course takes place in The 50-80's era Aperture from the sixth and seventh chapters of the singleplayer
Course Six: Art Therapy
Set after the conclusion of the Mobility Gels course, GLaDOS has reassembled the bots for testing again and claims that it has been 100,000 years since they were last reassembled. As the testing progresses, the bots are able to observe the defunct surroundings of the Enrichment Center, which GLaDOS assures them as part of an "art exhibit". Further on in the course, players will be sent to a Robot Assembly Annex station to repair their own reassembly machines as GLaDOS finally makes it clear that it has only been a week since the Mobility Gels course and that she needs their help in restoring her control over the facility as something is overriding her controls. At the end of the course, both players are sent out of the testing area to resolve the problem in a control room housing a prototype chassis of the central core. While the first 8 test chambers take place in the "Remaster" clinical look, the last chamber takes place in the 50-80's era Aperture
Interestingly, the sixth course was initially going to consist of advanced test chambers during Portal 2's development, months before the game was released. However, this was scrapped and was removed from the final game. The Peer Review DLC to Portal 2 instead adds only challenge modes to single-player and co-op, with no sign of advanced test chambers. The Art Therapy course is referred to as an additional course instead of the "sixth course".
All owners of the Portal 2 Sixense MotionPack DLC receive this course for free. It makes use of the new Portal Surfing and One-to-One mechanics.