If the user is able to log in, but unable to see the videos, this might be happening for two reasons:
1. Their user has not been added to any classroom
2. Or they have more than one account and logged in using a different one than the one added by the teacher
Check to see what email they are using to log in, and which email has been added to the classroom.
If by any chance this doesn't work the teacher should reach out to us for assistance here.