For grade challenges, I have included a statement in my syllabus explaining that a grade represents achievement, not effort, and does not signify anything about the student’s potential or skills in any other area; my typical grade distribution for the course; and a statement about the difference in meaning and procedure for requesting an explanation of a grade (asking how to improve) and requesting consideration for a grade change (must be done in writing with evidence). Those things combined with a rubric for the main assignments have dramatically decreased the complaints I deal with. I don’t like to get into an unpleasant interaction with a student, so I’m big on prevention. That might not work with your students, of course.
from Kedves