This is an old thread, but the issue raised is ever green
To speak or not to speak... not speaking even when we know the answer, not speaking when we are not sure whether we are right or wrong, not speaking because we are lazy to think of something to say, not speaking because we don't want people to have certain opinion of us... these are inner obstacles which we can overcome.
Speaking up is important for both the student and the teacher. If we don't speak up and reveal our depth of understanding of something, how can the teacher correct us or teach us something above our current level of understanding?
I used to teach high school physics... i found it quite exasperating when i ask the teens questions and no one wants to answer, or they reply with nonsense! i'm not sure which is worse... The smart ones don't want to answer because they don't want to look like a brown noser or mr/ms know-it-all, the lazy ones don't want to answer because they don't want to think, the not-so-smart-ones act as though i am not talking to them, and the naughty ones answer rubbish because they want attention!
To me, i was not expecting anyone to give the right answer, but rather i wanted to gauge the group's level of understanding, or just wake them up. Asking and answering questions to a group is just another method to help everyone learn from each other and see different perspectives. This method can be a very effective learning tool, but only if people respond to the questions.