You may have students who attend your school and another institution. These are called dual-registered students. You can see how to record a student as dual registered here.
Managing which registers the student is in
For registers, there are two options.
Add Planned Absences
In this case, the student will still appear in registers, but they'll already be marked as absent. You can set a repeating Planned Absence to fill in the register with the D code for this student.
Only have them enrolled into the registers they attend
You can add a Timetable Slot Student Exception to remove the student from the timetable slots and registers when they are not due to attend your school.
Please note that using this method, they will not have any recorded attendance for these sessions. If they are not in your school for a whole morning or afternoon, they will not have a Roll Call statutory attendance mark reported in the census.
What happens if a dual registered student is excluded?
When exclusion is logged, this creates a planned absence with the E code. If there is a planned absence in already (such as to mark the student as D when at the other school), it won't override but we'll let your Attendance Officers know: Alert for Attendance Officers
However, in this case you should not remove the D codes. This is because the DfE advises here that "Where a pupil is dual registered, suspension sessions are not recorded for the day(s) they are attending the other organisation."
So if the whole exclusion was 10 days long, but the student was only due to attend your school for 5 days, Arbor will output that the exclusion was for 5 days.