Those tables hold students' data, and they have probably been even more active than the faculty. The question_attempts table holds the questions each student attempts and the conditions under which each individual attempt is made. The other tables would have the students responses, grading details, etc. The size of these tables will grow with the number of students and the number of attempts.
The good news is that you can reduce the size of your database greatly by developing a reasonable policy for archiving student data and deleting it from the database when instant access to it is no longer needed.