It bothers me when I tries to remember how many highschools or universities use curve to adjust the final grade for their student based on the class average.

I know failing the entire class would be unacceptable for the faculty that taught the class but watering down the materials or curving the grades to fit the standard was it necessary? What if there are few outstanding students that are ahead of the curve? wouldn't it be unfair to them if the curve was adjusted to the class average?

Sometimes, I started to question education standard for grading. What are the standard?

Knowing the materials and able to apply them?

Putting all relevant summary on one test paper?

Giving homework that count towards grade?

Quizzes to remind student how well they do for that subject?

If above are all taken into consideration. Why are instructors still applying the curve to adjust the class average.

  • 5
    I wouldn't call curve-grading a standard without specifying the locale, since it is not generally applied. In some countries it's common, in others it's not. Mar 31, 2016 at 20:17
  • Related: What does an optimal grading distribution look like?
    – ff524
    Mar 31, 2016 at 20:37
  • It is likely a combination of pressure for good evaluations, more so with non-tenured professors, and student pressure. I see curving as unfair to students that are successful in the course. It may not be an issue in small doses, but grade inflation via curving can seriously effect grad schools' abilities when it comes to accepting one student over the other. The inflation can have serious effects in the workplace as well.
    – Devin
    Apr 1, 2016 at 18:28

2 Answers 2


Instructors often use some kind of curve to adjust for the varying difficulty of exams from one year to the next.

The general idea is that if (for example) the class average on an exam is lower than it has been for the same course in previous years but the quality of the students' work is the same, then the exam given this year might have been more difficult than the exam in previous years. It would be unfair to students (and also reduces the signaling power of grades) if their grade is strongly dependent on the year in which they happened to take the course. An instructor might choose to adjust the students' grades to account for this.

It's generally unwise to assign grades in a way that is strictly norm-referenced, without taking into account the students' demonstrated mastery of the course material, for reasons described in this answer. For example, if the class average on an exam is lower than it has been in previous years, but the average quality of work submitted by students is also worse than usual, then the average grade of the class should be lower (to preserve "fairness" and also the signaling power of grades.)

Some instructors might use a curve for other reasons, e.g. if their department has a policy about the maximum number of "A" grades an instructor can give out. (Like this example.)

  • However, instructor does not curve down the exam.....only the scale is upward.
    – logger
    Apr 1, 2016 at 13:26

Almost all classes (in the US) are "curved" in the sense that, at some point, a numerical score on tests and homeworks has to be converted into a letter grade.

The distinction is between classes that are curved a priori—in which the function mapping numbers to letters is fixed in advance—and those which are curved a posteriori—where the function is picked after looking at the numbers.

ff524's answer explains why many professors prefer an a posteriori curve. Many professors guarantee a certain minimum in advance: say, f(90) is guaranteed to be at least an A-. This is mostly customary, and students seem to like it. Furthermore, in many (maybe most) cases this promise is meaningless, because the metrics are written to guarantee that this would happen anyway. (Indeed, one advantage is that it reminds the professor that grades shouldn't "clump" too tightly: it's a bad thing if f(90) is a C+ and f(92) is a B.)

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