Note that this option is (or will be) only available if you are using a nickname for the class. It will not work for meets scheduled as Calendar Events.  The nicknamed meeting should be created just before the meeting starts, but students can be told the nickname ahead of time. This is the announcement: Hangouts Meet improvements for remote learning. 

• Meeting participants will not be able to re-join nicknamed meetings once the final participant has left. That includes:
  • The meeting was created using a short link like g.co/meet/nickname 
  • The meeting was created at meet.google.com by entering a meeting nickname in the “Join or start a meeting” field 
  • The meeting was created in the Meet app by entering a nickname in the “Meeting code” field

The same nickname can be used by multiple teachers, and gives them owner access to the Meet, students can’t enter the Meet until a teacher has created the Meet. The link/URL to the meet is deactivated within 5 minutes of the last person leaving the Meet. 

For example:  If you advise students that Mr Clark’s 11th grade class on biology has a nickname of “clark11bio”, then they just need to enter the nickname when the meet is scheduled. And as long as Mr Clark has already created the Meet using the nickname, they will be able to enter. This can also allow other staff to cover for Mr Clark if they are unavailable, without having to send out new links or info to students.