When participation is not required, chances are students won't participate. Also let students know when you will participate if you do not plan to check in daily. For other activities, e.g., research projects and discussion of course materials, small groups of 3-9 make more sense.
Groups can also work together on summaries, projects, papers, etc.
Promoting Critical Thinking Discussion can be used to help students reach conclusions, make decisions, draw inferences, explain causes, make predictions, reflect, analyze, compare and contrast, reason, and solve problems. Diagnosing and checking. Recall of specific facts or information. Structure and redirect learning. Encourage higher level thought processes.