Grading on a curve is standard practice on many college campuses–and it’s long had plenty of fans, as well as plenty of detractors. While it can promote more participation in certain subjects, it can also produce undue competition between students, and create more work for instructors who don’t have much experience with curved grading.

Here we’ll discuss what it means to grade on a curve, the advantages and disadvantages of doing so and some of the best practices for instructors who want to learn more about it.

What is Curved Grading?

Instructors will grade on a curve when they want to have a specific distribution of scores, also called “normal distribution.” To ensure there is a specific percentage of students receiving As, Bs, Cs and so forth, the instructor adjusts students’ grades.

When recorded graphically, the distribution of grades ideally forms the shape of a bell. A few students will do poorly, a few will excel and most will fall somewhere in the middle. Students whose grades settle in the peak of the bell are those students who received a C-average. Students with the highest and the lowest grades fall on either side of the peak. 

Some instructors will only grade tests on a curve if the entire class struggled with the exam. Others use the bell curve to grade for the whole semester, combining every score and putting the whole class (or all of their classes, if they have more than one) on a curve once the raw scores are tallied.

Benefits of Bell-Curve Grading

Ideally, a test should not be too hard nor too easy. Grading on a curve with a standard deviation gives instructors an at-a-glance look at whether the test was too hard, too easy or just right.

Curving grades also allows the instructor to have the same distribution of grades in every class. Morning classes, afternoon classes, online and in-person classes will all fit the bell curve, regardless of the breakdown of the original raw scores.

An instructor may use the bell curve when teaching large classes, with hundreds of students. A larger sampling of students provides a more accurate picture of students’ capabilities, and classes of this size play to the strength of the bell curve.

Curved grading benefits students both broadly and narrowly. In some cases, curving grades may mean that some underrepresented populations wind up in a classroom they wouldn’t be in otherwise. For example, an article on the Inside Higher Ed website suggests that classes that are graded so that scores are weighted toward a “B” would boost participation in STEM subjects by 7.2 percent, and participation among women by 11.3 percent. And any instructor would agree that more participation is better.

Disadvantages of Grading on a Curve

One of the advantages of using the bell curve can also become a disadvantage. When instructors grade on a curve, students’ grades aren’t looked at by themselves. Rather, they are seen as part of a whole—one student’s grade is relative to every other students’ grades.

While some students might work harder to see if they can get a better grade, this can also create unhealthy competition. Either the best students won’t take the time to help those who are struggling, or they feed false information to their classmates to get ahead at all costs.

This competitive atmosphere can also breed mistrust if most of the people in a class do poorly on the test, they’ll wonder who threw off the curve. This can happen when one student earns a very high grade, like  99 percent, while most of the class earns grades in the 70s. It would be difficult to curve the grade no matter how good one’s grading scale calculator is. 

Trying to grade on a curve in small classes is also difficult. The college grading scale calculator can favor classes with 200 or more students, but the opposite can be true in smaller classes, with the cutoffs between As, Bs, Cs, etc., being only a few percentage points apart.

How to Grade on a Curve

If, after weighing all the pros and cons, the instructor decides to grade on a curve, there are a number of formulas for curved grading to choose from. Some grading formulas are quite complicated, while others are simple.

One popular method is to use a grading scale calculator. The instructor uses a square root of the raw score, and multiplies that number by 10. If a student gets a 90 percent, the instructor divides that by the square root of 90, about 9.5 e, for a result of 9.47. Once that number is multiplied by 10, the student’s score becomes 94.7 percent. This allows the scores in class to be raised without going over 100 percent.

Another formula for grading on a curve is much simpler. First, assume the ideal grade is 100 percent. If the person who gets the highest grade in class receives an 88 percent, that becomes the de facto 100, and the instructor adds 12 points to the student’s score. The instructor then applies 12 points to the grades of all students in the class.

Instructors who’d like more help keeping track of their grading systems can use Top Hat. It includes a college grading scale calculator, which is especially helpful for instructors who don’t have much experience with using a bell-curve grading system.

Is Grading on a Curve Right for You?

Many instructors grade on a curve for good reason. It allows them to see if they’ve created a test that isn’t too easy or too difficult. It makes it easier to grade large classes and to grade more consistently across all of the instructor’s classes. It’s also a way for instructors to get feedback about how they create their course curricula.

Additionally, studies have shown that some subjects, like STEM subjects, benefit from a curved grading system, encouraging greater participation. That said, the practice does have its downsides. It can promote unhealthy levels of competition between students, and create mistrust and conflict in the classroom if students with lower grades accuse higher-achieving students of throwing off the curve.

It also doesn’t always work well when classes have fewer than 100 students. In these cases, the differences between the students who get As, Bs, Cs, etc. may be too small, sometimes only a few percentage points.

Finally, some instructors aren’t used to curving the grade, so they need to learn the formula for doing so. They can apply a simple plus/ minus system or a more elaborate square-root system. Regardless, whatever method of grading they decide to use, they should take both the pros and cons into consideration before they settle on a grading method for their classes.

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