Can a Student be a TA or Grader or edit the course?
Student, TA and Grader are all Primary roles.
A user cannot have more than one Primary role. See Roles miniguide.
It occasionally happens that the TA or Graderis registered to the course through Minhal Talmidim, or that one of the Students must manage the course page.
A user with enrolment type of auto (i.e. a Student registered through Minhal Talmidim or a Teacher or TA listed in the Shnaton) cannot be unenrolled from Moodle.
The solution is to assign the Student a secondary role of Grading and/or Editing: