So that still breaks down the same way. A class will have a relationship with multiple students. And a student will have a relationship with multiple classes. So, the way to get that done is an interim table, one that connects the two together through a many-to-many relationship. Then, you're probably going to need a marks table that is related back to the StudentClass table. Now that one could be slightly harder to set up due to the fact that I assume there will be multiple marks per class. So, you'll need another table, we'll call it MarksType, that designates what any given set of marks is. You could also add another table called MarksPeriod (or something like that) that designates the time frame, end of quarter, end of semester, mid-semester, whatever. Then, all that will be the identifying key for the marks table so that for a given class and student, for a given mark type, for a given time frame, they get one grade.

But, that assumes a lot that you haven't stated. But you should be getting the idea of how to start to lay stuff out. When you have the tables put together and a specific clarifying question, get on back to us.