Why is a teacher's Class Attendance page not listing the students in alphabetical order?

The Classroom Attendance page has the ability to sort the roster by each column heading and in ascending or descending order.

When clicking on any column header, an arrow will display to the right of the column header name. 

The arrow notates which sort order is happening; ascending or descending. 

This is an example of sorting on the Name column. The arrow is pointing up and the sort is alpha order ascending by student last name.

Clicking on the Name column header again will place the arrow in the down position and the sort will become alpha order descending