>As an aside, I'm surprised oral exams aren't possible at 36 students.

It depends on how frequent and how in-depth you want the exams to be. How much knowledge can you test in an oral exam that would be similar to a two-hour written exam? (Especially when I remember my own experience where I would have to sketch ideas for 3/4th of the time alloted before spending the last 1/4th writing frenetically the answer I found _in extremis_).

If I were a teacher, my experience would be to sample the students. Maybe bias the sample towards students who give wrong answers, but then it could start either a good feedback loop ("I'll study because I don't want to be interrogated again in front of the class") or a bad feedback loop ("I am being picked on, it is getting worse than I can improve, I hate this and I give up")