It's been some time since I checked in on student related stuff, but..
IIRC PSDs contain some process related information that instructors check on; like for example photoshop layering contributes to file sizes and they don't want their students abusing it to the point of large file sizes; it'd look bad for their school's reputation.
do instructors really require people submit PSDs or do students export their stuff to jpg/png/whatever and submit the export