Parents, please note that you may request to be added to your child's classroom at any time by simply e-mailing a teacher and providing them with the best e-mail to receive summaries. While you may provide any e-mail address, Google Gmail accounts allow you to manage the content and frequency of the e-mail summaries you receive. Once any teacher adds you to their Google Classroom as a parent/guardian, you will be automatically added as a parent guardian to any other Google Classroom that your child is a member of.
https://support.google.com/edu/classroom/answer/6388136?hl=en&ref_topic=7175351