Grading on the Curve
This method of assigning grades based on group comparisons is complicated by the need to establish arbitrary quotas for each grade category. What percent should get A's? B's? D's? Once these quotas are fixed, grades are assigned without regard to level of performance. The highest ten percent may have achieved at about the same level. Those who "set the curve" or "blow the top off the curve" are merely among the top group; their grade may be the same as that of a student who scored 20 points lower. The bottom five percent may be assigned F's though the bottom fifteen percent may be relatively indistinguishable in achievement.
Quota-setting strategies vary from instructor to instructor and department to department and seldom carry a defensible rationale. While some instructors defend the use of the normal or bell shaped curve as an appropriate model for setting quotas, using the normal curve is as arbitrary as using any other curve. It is highly unlikely that our college and university student abilities or achievement are normally distributed.
Grading on the curve is efficient from an instructor point of view. Therein lies the only merit in the method.