The best bet is to catch this early! The Executive Dashboard displays an alert for the previous day's classes that did not have complete attendance taken in the Staff Portal. Keep an eye on this alert daily to stay on top of Staff Portal Attendance.
Use the link in the alert to take you to the detail of which class(es) were not completed for the previous day. You can enter a different date in the search field of the Date column to view another single day or you can generate the report for a range of dates from the Reports menu > Staff Portal section.
In order for a class to fall off of the Incomplete Portal Attendance report for any date, the attendance must be completed in the Staff Portal.
Use the Portal Msg link next to the class to create a Staff Portal login message that the instructor of that class will see when they next log into their portal, reminding them to complete attendance for the class. If you are set up for text messaging in Jackrabbit you will see a link to send a text to the instructor.
If the attendance needs to be completed right away you have the option of logging in to the Staff Portal and completing the attendance for the class yourself (You must have a login ID that is permitted to manage other instructor's classes. See Attendance Settings). You could then use the Portal Msg link / Text Msg link to let the instructor know that you have completed attendance for them.