Another cool learning tool would be to mix the song in two parts. Part one would be everyone on their own. Those mixes would be uploaded and locked down, but not listened to yet. Part two would be everyone gets J's mix of the song, then starts from scratch (no cheating) and mix again. Then upload and compare both mixes, and discuss how after listening to J's mix how you changed your approach and blah blah blah.
Just a thought. Interesting study of psychology and hearing and stuff.