When students get replaced by changlings and either fight/find their way back or get returned at the end of the year, what happens to the grades they got whist gone? Do the changlings attempt to do the work and is that the missing student's grade for the work they missed or do they get to retake it? What happens if the changlings don't do any of the school work?
Changelings usually attempt to do the coursework in the real student’s absence, with varying results. If you’re unhappy with the grades they got, you can petition certain officials for a chance to retake the tests/write better papers. It’s also occasionally possible to retake the course in its entirety; once in a while the Library will hold remedial courses in the Velvet Room, one of the few rooms where time is a bit out of whack yet still cleared as safe.