How can I use relationships to auto-create records in my subform?

### How can I use relationships to auto-create records in my subform? ###
Please Help!

Using Access 2007, I am trying to create a "Classroom Database" where I can
manage students and grades (for one class). I have created the following

tbl.Student
-SID (auto)
-LastName
-FirstName-
-StudentID
-Comments

tbl.Assignments
-AID (auto)
-Date
-Assignment
-Notes

tbl.Grades
-RID
-Student (looks up student ID)
-Assignment (looks up assignment)
-Grade (%)
-Note

Thus far, I have created two forms (each with a subform), one which allows me
to open up an assignment and see grades by student, and another where I can
view all of a students grade.

### My question, and I have seen this before, is that I would like ALL of the
students to be added to each assignment automatically. As it is now, I need
to add a new record for each student under each assignment (grab their name
from the dropdown list). How can I setup the subforms to automatically
propogate a GRADE record with each student name and a blank Grade field? ###

Thank You! Jared