1. Ensure a Non-Attendance Reason is setup to be allowed for use in the Customer Portal.
Go to Configuration -> Non-Attendance Reasons
Edit or Add a Non Attendance Reason, ensuring the 'Show in Customer Portal' option is enabled for the Non-Attendance Reasons you wish to make available on your Customer Portal.
2. Set the Days in advance for Non-Attendance
Go to Configuration -> System Setup -> Customer Portal. Enter the number of Days in Advance a Family can enter their Non-Attendance. Also ensure the 'Disable Non Attendance' is not ticked. (Ticking this field will DISABLE the Non-Attendance module in the Customer Portal).
When you have completed the above configuration, your Customer Portal will display a section to allow a family to record their own Non-Attendance information.