In Office 365 you can include all the students in a single class into a Mail Enabled Security Group and simply send one invitation.
Navigate to Exchange Admin Center (if you create it from the user portal, the SG will not be mail enabled)
Click the + sign an Select Security group
Fill in the form and Select members
Make sure to check delivery management and enable so that users outside the organization can send mails to this group. If you do not do this then the sharing mail will not be sendt.
After you created the group, allow for some time for the mailbox to be provisioned. while waiting, insert a mail tip by selecting the SG and click pencil.
Then Navigate to OneDrive and Select Your file to share
Log in on a user to verify that the mail has been sent successfully
Note on a limitation.
This file does NOT show up under “Shared With Me” tab in OneDrive. This is a platform limitation at the moment. They can browse Your profile and see it or use the email to Access it.
Create a link in a gallery on sharepoint for files to Your classes