Most people who have taught a seminar-style class have probably struggled with the issue of how to get everyone to participate. I face this issue in freshman seminars and in graduate seminars. I enjoy the challenge of getting freshmen to speak in a seminar -- most freshmen have never had a discussion-type class and need some help to feel comfortable speaking in that type of environment (especially the female students). With lots of friendly encouragement, class participation is typically high by the end of the semester.
In graduate seminars, participation is hugely variable. Some first or even second year students need time to feel comfortable, but even then, some grad students never say much, if anything, in seminars unless forced to. I am very inconsistent from year to year in terms of how I deal with this. Some semesters, I don't do anything more than assigning a student to be the discussion leader each week. Other semesters, I am more controlling about the format, so that everyone has to speak whether they want to or not. In the more free-form format, it's interesting how frustrated the discussion-leaders get with their fellow students who don't participate in the discussion or who come to seminar unprepared. For some, this is a wake-up call, and they come prepared to participate in subsequent weeks. Some slip back into their quiet and/or unprepared mode once their major responsibility is over. I think this says a lot about a student's motivation, though I prefer to form my general opinion over the course of the entire semester, not based on any one week (everyone has busy weeks).
A seminar with lots of discussion is a more interesting seminar, but my desire for a lively discussion is balanced by my wish to have the students take responsibility for themselves and not be forced to contribute if they'd rather just sit in a torpor. I make it clear at the beginning of a seminar that my expectation is that everyone actively participate in discussions every week and come to class prepared (i.e., having read and thought about the papers to be discussed, and ideally with questions or comments to discuss). Some students do this and some don't.
I like assigning or asking for volunteers for discussion-leaders in advance because these students tend to do an excellent job preparing and seeking out additional background information to bring to the discussion. When this system works, it works well. I had one student recently, though, whose idea of leading a discussion was to say "So what did everyone think of these papers?" and sit back and hope that everyone else had something to say.
Some of my colleagues use various techniques for 'inspiring' participation. One colleague doesn't announce in advance who will be the discussion leader, then he chooses someone (or has a random drawing) at the beginning of each class. Students tend to prepare well so that they won't be humiliated, but my colleague admits that some students prepare the minimum anyway, and he sometimes ends up leading the discussion himself.
Grades shouldn't be the main motivator for grad students, but in a pass/fail seminar, some students seem to think that they will pass if they just show up often enough. Perhaps if they knew they would fail if they never participated in discussions, this would help motivate them, but I haven't yet wanted to go that route.
I am sympathetic to new students who need some time feel comfortable in seminars. I can remember how I felt as a new grad student in a seminar dominated by aggressive male students. It was very difficult for me to speak up. I eventually solved the problem by talking to the other students informally before the seminar about the discussion topic. I found that they were really only aggressive in the seminar, where they were vying to impress our advisor. Outside of seminar, they were very happy to talk to me, and very patient about answering my basic questions. As a result, I felt more comfortable in the seminar, and started participating more.
I don't feel that I've found the ideal solution to this perennial seminar issue, but I've decreased the problem a bit by giving students a say in seminar topics and by making each student responsible for some of the discussions. I'd be interested in hearing any new ideas to increase seminar participation without resorting to control methods that essentially force students to participate.
7 months ago