This can be caused if the Students who do not appear on the Class Schedule have a future Enrollment Date. You can check this by taking the following steps.
  1. Got to onRecord
  2. People Finder
  3. Locate Student not showing on Class Schedule
  4. Click on their Enrollment Tab
  5. Locate the Course and check the Begin Date
  6. If this Date is in the future they will not show on the Class Attendance