I know this may seem counterintuitive. Allow me an explanation. I have found in many courses that group work of 4 - 5 students seems to increase participation as many already know. I also find that it allows students the opportunity to formulate their interpretation of the subject matter. Also, a known impact. How many of us on the teacher side have stopped to look at the impact it has with relation to the students. I have a theory. I think students are more accepting of ideas and feedback from the instructor because they are surrounded by peers sharing like experiences and this raises their individual comfort levels.