This is because Nickname is not set to display to Parents. To set profile publish access, navigate to:

1. Core > Security > Profile Access
2. Select Profile Publish Access
3. From the drop-down menu, select the role for which you would like to publish information (Student)
4. Click the role-to-role link to publish that role's information to another role (Student to Parent)
User-added image
5. Click Edit
6. Select the Radio button for "Reset Publish Fields for ALL Users"
7. Mark Nickname and Middle name
8. Click Save & Confirm
9. Click Confirm
10. Click OK