Students in these courses have already had several courses together and know each other pretty well, so I have not felt the need to address this issue. Both a. and c. are successful, although success varies with different classes I would not term everything I do an assignment since they are not always to be turned in. In our Basic Statistics course the final exam was a poster presentation of a semester-long project involving the design of an experiment and then the collection and analysis of the data. If the activity is carefully planned and laid out, then it generally goes better. Some difficulty in getting all team members to participate, and being sure this in fact happened.
Students tend to depend far more on each other than on the instructor.