How a numerical scale, if used, translates into letter grades is left up to the discretion of the individual teacher. All grades need to be understood in the context of the individual student's developed abilities, which obviously vary from student to student, from course to course, and even from assignment to assignment. Just as students' capabilities for academic achievement varies, so, too, do their levels of commitment to the academic enterprise. Sometimes an otherwise exceptional student's attention and engagement may come and go, or perhaps a student may focus more on finishing work than on understanding ideas. The grade a student earns for an assignment or for a course will no doubt be influenced by these factors.
Grades are useful in helping students plan their overall academic programs.
Many of the choices students make about the courses they take should be influenced by performance in previous courses since that performance is a legitimate assessment of the student's readiness for subsequent courses. It is not intended solely as an incentive or reward for students to enroll in demanding courses.