Your relationships would need to change before an assignment record that is not linked to student via a corrected assignment record. Perhaps the easiest solution would be to set up your system with a script to automatically create records in corrected assignment when you create a new assignment record for a specific class (or subject).
That's a good idea and I did that with attendance. If I cannot make it any other way I guess I'll go with it, but I would prefer if the teacher created every correced assignment individually so I wouldn't have any "empty" corrected assignments. What would you say would be the keyword for figuring out how to change the relationship if I would go with that? Can it be fixed with another Table occurrence, for example?
The problem I see with that is that for many teaching environments, you really do need that many to many relationship as a given assignment can be assigned to many students and a given student will be assigned many different assignments.
As someone who tried their hand at teaching for a few years, I'd actually prefer that "empty" corrected assignments record. That empty record would document the fact (and the date) that the assignment was assigned to a specific student. (It's not uncommon for some assignments to not be assigned to all students. Some may, for example, be extra credit projects.) Fields within the record would then be updated to record relevant info about that assignment (such as a score or grade) that would also indicate that the assignment was turned in and corrected.