This is only possible, of course, in small classes. Ask students to write a question or pose a problem that they were well prepared to answer. A variation is not to give students a take-home test but instead to schedule, some days later, a repeat test containing equivalent items. After making some general comments on how the class performed as a whole, you can show the general distribution of scores, note items missed by many people, and correct widespread misunderstandings. For essay tests, describe what you expected in a good answer and the most common problems.
Some faculty read or distribute unsigned excerpts from outstanding papers.
She reports that having students review exams in groups often takes less time than her own reviews and students report enjoying it more.