OneNote Class Notebook add-in already includes assignment and grade integration, connected to a Learning Management System (LMS) and Student Information System (SIS). The OneNote Class Notebook now integrates assignments and grades with over 40 LMSes and SISes and Microsoft is planning to add more in the future.
Yesterday, Microsoft announced support for Blackbaud onCampus and eSchoolData with the updated Class Notebook add-in. Microsoft has also included assignment and grade improvements for Google Classroom with this update. Class Notebook add-in version 188.8.131.52 also includes bug fixes and stability improvements.
You can learn more about it here.