To repeat Students after Promoting navigate to:
  1. Core > Users > Edit User Profile Data
  2. Search the User
  3. Scroll Down to System Information
  4. Click Student Enrollment
  5. Click Edit for the Year the Student is Repeating and Change the Grade Level to the Same Grade Level and select the Repeat box.
  6. Save & Exit
For example: you have a user that is currently the class of 2016 Repeating the 2015-2016 12th Grade
Click Edit next to the 15-16 School Year
Select the 12th Grade for the Grade Level
Select the Grade Repeated checkbox
Save & Exit
This will move the Alumni Affiliation to the next Year (in the above example 2017) and move all future enrollment rows up a year so he will have 12th Grade for 15/16 and 16/17.