Not necessarily final grades in the class. Also, I have no indication for how he did in his non-major classes.

There was a tight knit group of people in my Engineering undergrad that were all on the same graduation track, and it was pretty normal to hear through the grapevine who scored what on the exams. From what I understand, the Marriott School's undergrad Finance emphasis is very similar (small and tight knit). I have not asked my friend how he found out, but I'm sure word traveled fairly easily. Plus, it's pretty easy to tell by the kinds of questions someone asks in class whether or not they're grasping the concepts.