Scaling is an issue for sure--just having the time in the week is impossible without distributing the work to TAs, and administering oral exams is tough for TAs

Scaling is an issue for sure--just having the time in the week is impossible without distributing the work to TAs, and administering oral exams is tough for TAs. But you can do an oral exam along the lines of "explain to me how your project works" and that'll catch people who don't understand it regardless of whether or not they know the question in advance.