In my classroom, I always encourage my students to talk.  I walk around the classroom and monitor the content of their discussions.  I sometimes join in their conversations and encourage them to think deeper and more critically on topics of discussion or guide them with probing questions so that they can develop solutions to problems they may find difficulty with.  I also encourage them to be unafraid to make mistakes or give a 'wrong' answer.  I explain that if no mistakes were made, then there will be no need for learning.  They should instead analyze the types of mistakes they make to reveal the gaps in their understanding.  This also informs me of what I need to teach.