How to Assess Students in a Socratic Seminar?

I think it's really important to provide students with the rubric before we go off and have our discussion. So what they are being assessed on is their level of understanding of the text, how well they analyze it. And then are they using evidence from the text? I just print out all my rubrics. I already have my students' names on them. It's just quick and easy. You can see what questions or what observations did they come up with as you walk around.