Some classes you will always have a couple students who do not want to participate - this is a given. I teach in generally small groups due to the nature of the courses and recent addition of the major. It's not unusual for me to have only five, seven, or ten students. While you would think this would be ideal for small group discussion - getting these students to talk is very difficult. So (this is a lecture and theory class which has a new essay due each week) I started including a presentation portion to the essays. Instead of just a write-up and group discussion - now there was an individual PowerPoint presentation due with the essay - highlighting the main focus of their own essay. This actually seemed to help one particular group - who came to know each other better - and if they were nervous - we'd always start with a quick - light-hearted intro about the slide design on their PowerPoint - before getting into the heart of the discussion. So, I've become a firm believer in the small group (since the class itself is a small group) discussions. Great way to encourage silent students.