One of the chief roles of a teacher during a time of discussion is not to assess who is right or wrong but to keep the discussion on target. Discussions can easily stray into talking about pet peeves if they are not guided correctly. Often guiding the discussion is done with questions that bring the speaker back to the discussion topic. You can say things like, “What you have said is good, but how does it help us to understand our topic?” If you summarize the contribution of each speaker to the topic, it may help later speakers to stay on the topic.