Dear Jacklyn,
Good day!!
Apologies for the inconvenience caused and please don’t worry, let’s work together on your concern and move towards a resolution path.
I understand your concern and to my knowledge, I would like to convey that the behavior you are encountering with one of the Class Notebook is not an expected because Teacher Only section in the Class Notebook is only for the teachers who are added to the Class Notebook.
In the backend the Class Notebook is structured as a folders, two possible reasons for the students accessing the Teacher Only section is either the Teacher Only folder is shared with the students or students are added as a teachers in the Class Notebook.
I believe the later scenario is not possible and to check whether the Teacher Only section is shared to the students in the Class Notebook, I would like to request you to follow the below steps in the owner OneDrive for Business who created the Class Notebook: View Class Notebook folder structure in OneDrive - Microsoft Support
Note: If the Class Notebook is created view Class Team in Microsoft Teams, go to respective SharePoint Online site associated with Class Team and search for Teacher Only in the search bar of site to see whether you are able to find folder of Teacher Only.
If you are able to find or view the Teacher Only folder of the Class Notebook, then right-clock on the folder> Manage Access> Check in the Links and People tab to find if it’s shared> If no, click on the three dots in the Manage Access> Advanced Settings> Check Permissions> Enter the student email address> Check Now.
If there is no success in finding the Teacher Only folder or it’s not shared, I am sorry to convey that the problem should be further investigated by the related development team, where they can collect the HAR logs while reproducing the problem and perform further investigation.
Note: I have checked the service health dashboard at the Microsoft end, where there is no related incident found.
So, I request you to connect with your IT admin of your organization (How do I find my Microsoft 365 admin? - Microsoft Support) and raise a new service request from the Microsoft 365 admin center so that the related development team will connect with you and investigate the issue further.
Reference: Get support - Microsoft 365 admin | Microsoft Learn
Note: We apologize for redirecting you to related development support team because the moderators in this community are limited with the resource for further investigation and to get a quick resolution to your problem, we requested it.
Appreciate your patience and understanding. Have a great day!!
Best Regards,
Sophia