When a student moves from one course to another, their grades do not follow students to the new course. Teachers can export students' grades from the original course and import them into the new course. Assignment submissions and assessments will remain in the original course.
If you use Google Assignment App, the assignments the students work on actually belong to the teacher and can be located in the teacher's Google Drive in their Schoology folder. Google Assignments initiated prior to the move will also be found in the student's Google Drive in their Shared with Me drive. Students can submit finished work either by submitting a link to the document in their new course, or create a new copy of the assignment and copy and paste their work from their original document from the old course into a new document in the new course.