Help! I CANNOT JOIN my teacher's GOOGLE CLASSROOM?

We understand how frustrating this must be. The problem is most likely a personal Google account on the device the student is using. To resolve this, the most sure-fire way is to REMOVE all personal Google Accounts from the device. The second alternative is to SIGN OUT of all personal accounts on the device. Finally, be sure to check that the student is in his DISTRICT Google Account every time he/she changes pages on the device.

Here is a video to watch for clarification.