The <addstudents> element configures optional elements of the Add Student dialog, which is invoked from the teacher's Gradebook.
<addstudents inviteurl="url" addurl="url"/>
addstudentsinviteurlCauses the "Invite Student" link to appear on the Add Student screen. Its value is the URL to invoke when teacher clicks "Invite Student".

addurlCauses the "Add Student" button in the gradebook to change to Add/Edit Student. Clicking the button invokes this URL, rather than the standard Add Student screen.
See Also
Domain Customization