The instructor has tested and reported that changing the user role to guest has an immediate effect and the account can't proceed with continuing the quiz. So a potential solution it looks like, would be to create a new role below guest level and assign to that student to prevent login. This has to be tested though to see if the student would get logged out immediately with a role below that of guest. The reason for this is, by default guest could still see the questions it seems. But would anything happen to the progress data of the student for assignments, quizzes etc before any role change happens? That is the main worry. Thanks.