What I usually do is aknowledge the students comment(s), then direct the discussion back to our focus. I try not to expand on what the student comments, just aknowledge it and move forward. If it reaches a point of disruption and can not be contained in the moment then it becomes necessary to "take a break". At this point I will pull the student aside and again aknowledge the importance of their viewpoint but that perhaps it is better suited for a discussiion at a later time, outside of classtime.
