Thanks for your thoughts, Joost.
As we move through the course, I regularly change the composition of the groups, as I want students to have the experience of working with different teammates. (They like it, too.) Groupings seemed to me to be the robust way to do that. I could instead simply switch people in and out of their initial groups, but there could be problems when we're in Unit 6, say, and a student wants to go back to a Unit 4 forum and say something: Her Unit 4 teammates might now be different, as might the entire discussion!
As we move through the course, I regularly change the composition of the groups, as I want students to have the experience of working with different teammates. (They like it, too.) Groupings seemed to me to be the robust way to do that. I could instead simply switch people in and out of their initial groups, but there could be problems when we're in Unit 6, say, and a student wants to go back to a Unit 4 forum and say something: Her Unit 4 teammates might now be different, as might the entire discussion!