If students get a notification that their username is not recognized during login, please tell them to add this to the front of the user name: "lw_student_"
E.g., if the previous username was "john12" the new one will be "lw_student_john12". Or "923student" then the new will be "lw_student_923student"
I hope this helps. We are working on a solution so students don't have to do that, but that should solve the logging-in problem for now.
If there is still an issue:
The majority of student's passwords should be the same, but on some occasions, you might need to change their password in the teacher admin panel: https://www.liveworksheets.com/t/my-students/all