Google Classroom Guardian Invitation
As a guardian, you must receive and accept an email invitation before you can receive email summaries. Only teachers and administrators from your student’s school can send these invitations. You have 120 days to accept an invitation before it expires.
The teacher emails you an invitation for a particular student.
The teacher can send the invitation to any email address.
In your email program, open your email invitation.
Click Accept.
If you’re not the guardian, click I’m Not The Guardian.
You can choose the frequency of the emails, such as daily or weekly.
You can unsubscribe or remove yourself from Classroom at any time.
Guardian email summaries include:
Missing work—Work that’s late at the time the email was sent
Upcoming work—Work that’s due today and tomorrow (for daily emails) or work that’s due in the upcoming week (for weekly emails)
Class activity—Announcements, assignments, and questions recently posted by teachers
See more details here https://support.google.com/edu/classroom/answer/6388136