The Registration Start Date is used to indicate when the Student School Enrolment starts (or started).
When the Registration Status is Registered, the Registration Start Date indicates the day the student is expected to start at the school. For most enrolments, this is the first day of school.
When the Registration Status is Active, Completed, Withdrawn, or Closed (Registration Status), the Registration Start Date indicates the student actually started at the school. For most enrolments, this date is not updated because the student starts at the school the day they expected to start at the school.