All active clients are listed on the Attendance screen. If clients are assigned to a staff, that has no bearing on whether or not they are included in the Attendance. However, the Program that is selected will determine the order of the clients.
In this example below, Yogi, Taz, and Fred are all assigned to the 'Community Employment' program. As such, they are at the top of the list. The remainder of the clients are then listed alphabetically.