I learned about this because a friend of mine from graduate school, Julie Anderson, teaches at a school that uses Harkness tables, and she was in a video about that; it's from an Edutopia profile of the school: Collaborative Learning Leads to Student Success. Julie starts talking about the meaning of the Harkness table around 3:50 into the video:
Here's what one of the charts that shows the interactions around the table. It's a "discussion tracker," and there is more information about that here: Collaborative Learning Resources. One of the students has the task of making the map as their contribution to the discussion:
Isn't that cool? There is a Wikipedia article about Harkness tables too!