Among the many confusing new things that you might hear in the first year of college is that your tests will be graded on a curve. What does that mean? Grading on a curve is a method that college teachers use to adjust the grades to make sure they have a normal distribution.

Grading on a curve has its advantages and drawbacks, so it is disputed in the academic community. It might mean that your grade is bumped unexpectedly upward, or it might mean that it's virtually impossible for you to get an A because you're being compared to other more successful students in the class.

Bell Curve Definition

In statistics, the bell curve is a symmetrical bell-shaped curve that represents the distribution of a set of data or values. The highest point in the middle of the curve represents the maximum probability. The bell curve establishes normal distribution, meaning that the data is distributed evenly across the sections of the curve.

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The bell curve method is the most popular method of grading on a curve. If you’re being graded on a curve that means that most of the students in your class will receive a grade that falls in the middle of the curve, which is a C. To ensure normal distribution, the teacher will assign only a small percentage of students to receive the highest and lowest grades. For instance, five percent of the students will receive As and Fs, 12 percent of the students will receive Bs and Ds, and the rest, 66 percent, will receive Cs.

Reasons Teachers Use a Grading Curve

Teachers use a grading curve in order to analyze their tests. Many teachers consider the test adequate if the bell curve is visible with absolute scores. For example, if the mean (average) grade of a test is C, and only a small percentage of students managed to get As and about the same percentage got Fs and slightly more got Bs and Ds, then the test was adequate. It was not too hard and not too easy.

If on the other hand, the absolute scores reveal that nobody got above 80, that might mean that the test was inadequately hard. In that case, the teacher might boost the student’s scores bringing them closer to the normal distribution, making sure that there are enough As and Bs to create a normal distribution.

How Grading on a Curve Works

There are several ways teachers create a test curve. First, if no one in the class scored 100, the teacher might take the highest grade (like a 90) and bring it up 10 points. She then adds 10 points to all the scores.

Another method is using a square root curve. In this method, the teacher takes the square root of the raw score for each student and multiplies it by 10. For example, the square root of 90 (rounded up to two decimal places) is 9.49. Multiplied by 10, the final score will be 94.9. With this method, lower scores will be bumped higher, but higher scores will not exceed 100.