At what point in your class did you realize that a discussion board that requires the participation of every student–at a quality level–is impossible for the 35th student who comes to the discussion thread. It really is hard to come up with something original and thought-provoking at that point. And it’s just as hard for the instructor to read through such a long thread.
What if the discussion is divided into groups, so that each group of 5 is only responsible for reading and commenting in that group’s discussion. It could be like the difference between a discussion around a table and one in a convention hall. Has this method worked for anyone?