After a student has been added to a class, if you remove the student from the class, his/her grades and attendance linked to that class will also be deleted.
Options are:
1. You can add the student to the new class "fresh" without any prior graded assignments.
2. The "new" teacher can manually add the graded assignments from the old class into the new class. The teacher can excuse the other students from those assignments using the Assignment Grade Code.