I apologize for not including links to previous blog posts on this topic. I forgot who sent me on this tangent. Feel free to add links in the comments.
Perhaps some students are quiet in class not because they don't have anything to say, but because they think what they have to say won't be seen by the teacher as the "right" answer. Even outside of the classroom, we often quell our comments for fear of being "wrong".
Maybe we could change that. Maybe we could make it perfectly clear that discussion sessions are not about right and wrong answers, but about exploring topics, fleshing out ideas, making mistakes. Mistakes are so important to the learning process, and if students were given the opportunity to make mistakes without it reflecting in their grade, perhaps they'd say more.
Facebook groups are one way to help overcome the reluctance to speak in class. Any other ideas?