Reason for Withdrawal will be collected for the first time in the Autumn 2015 School Census and is mandatory if a student withdraws from a course from the start of the 2015/2016 year.
There is no need to backdate if you have withdrawals in the 2014/2015 year.
The Reason lookup appears when you end a membership to a class through the Curriculum link in the student’s record.
Alternately there is an extra column (Reason) in Panel 7. Students and Memberships in a Course (Tools / Academic Management / Course Manager / Maintain Course) which can be updated.