Google's Guide - Link
To invite a group of students, you can use a Google Groups email alias. You don't have to be the owner or a member of the group, but you must be able to view group members and view email addresses.
- Go to classroom.google.com.
- Click the class you want to add students or a group of students to.
- Click People
Invite students
.
- Enter the student’s or group’s email address.As you enter text, an autocomplete list might appear.
- Under Search results, click a student or a group.
- (Optional) To invite more students or groups, repeat steps 4 and 5.
- Click Invite.
After you email the invitation, the class list updates to show the names of invited students.