Students should not by default be able to see this tab, so a permission must have been changed for the authenticated user or student role. Alternatively - is this a custom link, which was added manually from Site administration > Appearance > Advanced them settings > Custom menu items?
Mary Cooch (personal account)
Posts made by Mary Cooch (personal account)
Why not look at Site administration > Users > Assign system roles and see if there is anyone added to the non-editing teacher role site wide, and check the permissions of the non-editing teacher to see if they have been given the capability moodle/site:viewparticipants
Doesn't Moodle's built-in "Summarise" feature in 5.0 do that for a forum thread already? Or have I misunderstood you?

The student's message says "You cannot enrol yourself in this course" Was it a course with self enrolment or, as I suspect from your first post, he was enrolled into the course in some other way and can no longer access it?