First question - how do you think that went? From his/her answer I think you'll understand a fair bit about what kind of grasp they've got on their class. Questioning is how I tend to get through feedback (why did you decide to.. Tell me about X group there...) before concluding with my judgement and some solid targets as to what would take it to the next level.
We've been told never to start with "how did you think it went?" Partly because it's actually irrelevant - you're not going to change the judgement, and partly because it can make it worse if they thought it was good then you tell them it was RI. So, our process is - start by telling them the judgement, then go through the ways it would need to change to make it a good. Keep it short - 5 mins or so, then allow time for discussion at the end. It's hard, but easier if you stick to a formulaic approach.
I agree with this, Evil, but I do think you can get an awful lot from the "how do you think it went" question. If you saw several areas of concern but the teacher insisted it was great, you've got a problem.
Similarly, if you get someone who says "it wasn't as successful as I'd hoped, due to XYZ" then you know that even though they haven't had the best lesson, they're reflecting and will try something different next time.