Two other great quotes: "People have a strong gravitational pull toward feeling left out." and "Knowing something and not being able to articulate it is, in a discussion-based setting, the same thing as not knowing it."
Also, clarity in the syllabus and in the rules of the class makes everything easier, including but not limited to instances of cheating.
And important reminder is that the instructor must never submit themselves to the abuse of a student, and should step away if it ever comes to that.