Setting up tables for grades

I was thinking the problem was my tables. Here's my current structu

tblStudents:
StudentID
Last Name
First Name
Class #

tblCourses:
CourseID
Course

tblCourseGrades:
GradeID (Primary Key)
StudentID (Foreign Key)
CourseID (Foreign Key)
Grade

tblStudents has other fields, but those are the only ones that pertain to
setting up the grades. I know the naming convention for the field names
isn't proper, but I inherited the database and I'm afraid of changing the
field names because it might cause many other things to fail in the database.

Here's how my school operates:
Student shows up and is assigned to a class. The class takes the 13 classes
sequentially. A few weeks later some more students show up, are assigned to
a class, and they start the courses as well, taking them sequentially.
Hopefully that helps clear up what I'm looking for and expecting. I was
thinking I could just create a form that I could select the student from a
combo box, and the subform would list the courses and allow me to input the
student's grade for each class (to be stored in tblCourseGrades). Then I
would create report(s) that would allow me to take those grades and output
them in various formats (one individualized for the student, one for the
class, and then whatever other ones I get tasked to provide). I really do
thank you for helping me out and trying to make me understand how this is
really supposed to work.