Tools menu reference
Tools|Sort students|Group by class
The Sort Students Group by class command affects the student ordering when sorting alphabetically. Normally this menu item does not have a bullet to indicate the students are not grouped. If the menu item does have a bullet, when showing all students, choosing an alphabetical sort, either A to Z or Z to A, the students in the same class are grouped together and put in the order required.
Choose the command to set the grouping done with the next sort command. This command does not do the sorting; it only specifies whether to group the students by class when sorting alphabetically. If the students are sorted numerically the class grouping is ignored.