You did create ONLY a 1 to Many relationship.
Change it to a Many to Many, creating a join table between Students and Courses.
Here's a more detailed description of what raybaudi has recommended:
Students::__pkStudentID = Student_Course::_fkStudentID
Contributors::__pkCourseID = Student_Course::_fkCourseID
You can place a portal to Student_Course on the Students layout to list and select Contributors records for each given Students record. Fields from Contributors can be included in the Portal to show additional info about each selected Contributors record and the _fkCourseID field can be set up with a value list for selecting Contributors records by their ID field.
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained