Somehow the unfinished version slipped out of my computer while I was working on it and before I attached my signature block. My appologies for any inconvenience this caused.
Many students learn many things better by observing or listening rather than discussing.
Instead of a blanket statement that more participation means more learning, I think that we need to consider both the content of the course and the goals. For example, consider a course in computer programming. Some students will benefit from discussions, but others, the majority in my experience, will not find this to be an efficient way of learning. The only discussion necessary would be an occasional question. On the other hand, a course where the teacher does not have all the answers, a literature appreciation course, for example, would require a large amount of interaction between students as they explored various ideas.