How do I remove a student who no longer attends?

If a student no longer attends your school, you must DEACTIVATE them in their registration under the STUDENTS menu, as highlighted below:

Once this is done, their contracts will be canceled, and they will be removed from any class schedules they were enrolled in. If they have outstanding payments, these will remain until they are resolved! Any past records, such as payments, attendance, etc., will be preserved.