Students can be in more than one iCivics virtual classroom. Please note that assignments from one class will not show up in the other class. All completed assignments and game play will stay with that student's account unless the teacher deletes the assignment.
If you are looking to move a student from one class to another... Your student won't lose their data. They will see the game completions on their accounts but the assignments from the other class won't show up in the new class. The teacher will only see assignments from the old class as long as they do not delete the student(s) from the old class. Future assignments will be available moving forward in the new class. Because students can be in multiple classes, do not delete them from the old class if you want to continue seeing old assignments.