Bell Curve: Definition & Impact on Grades

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Chomsky's Nativist Theory of Language: Definition & Development

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:05 What Is the Bell Curve?
  • 1:17 How Grading on a Curve Works
  • 2:42 Standard Grading vs.…
  • 5:04 When to Use a Bell…
  • 6:32 Lesson Summary
Add to Add to Add to

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Login or Sign up

Create an account to start this course today
Try it free for 5 days!
Create An Account

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Jessica McCallister
You may have been graded on a curve in a high school or college class. This lesson explains the basic concepts behind the bell curve and grading on a curve, as well as their impact on grades.

What Is the Bell Curve?

Have you ever taken a high school or college class and were told on the first day that you were going to be graded on the curve? I'm sure you were left wondering, 'What does that mean? Will I get graded fairly?' These are often questions students ask when they are told they are going to be graded on the curve.

In this lesson, we'll explore what the term bell curve means and provide some examples of how it is used in grading systems. This is not a lesson in the statistical formulation of the bell curve; rather, it is a lesson to help you fully understand the impact on grades that the bell curve produces.

First, to help you better understand the basics behind the bell curve concept, let's start by explaining what the bell curve is. The bell curve is a statistical concept that is designed to establish a normal distribution. In a normal distribution, the data that is being distributed across the curved shape would be even. So, if you drew a normally distributed bell curve on a piece of paper and then cut it out, you would be able to fold it over perfectly. Its shape would be symmetrical. This is normal distribution, otherwise known as a normally distributed bell curve.

How Grading on a Curve Works

Grading on a curve impacts students' grades. There are different types of methods to grade on the curve, but here we'll discuss the most popular and classic method: the bell curve method. Imagine you were in class and your instructor said, 'Okay, this term you will be graded on the curve. The top 10% of students will receive an A, the second 10% will receive a B, the middle 60% of students will receive a C, and the bottom 20% of students will receive either a D or an F. It's up to you to work hard and try to earn one of those spots in the top 20%!'

If the grading is done that way for a class of 60 students, the grades will be distributed as follows: six students would get A's, six students would get B's, 36 students would get C's, six students would get D's, and six students would get F's.

Curved Grade Allotment (N = 60 students)
A's = 6
B's = 6
C's = 36
D's = 6
F's = 6

So the majority of students will be allowed to earn a C, and the grades, in this case, are normally distributed across a curve. On a bell curve like this, the top of the curve demonstrates the C's, the far right side of the curve is where the B's and A's are placed, and the far left side of the curve is where the D's and F's are placed. So, can you see which side of the curve you will want to be on in terms of receiving a grade? You want to be in the middle or right side of the curve!

A normally distributed bell curve
Normally distributed bell curve

Standard Grading vs. Bell Curve Grading Systems

Now, let's take a look at how this is different from standard grading. Let's say that in your class you were able to earn 1,000 points throughout the entire term. The points include tests, quizzes, papers, and class participation. In a standard grading system, you would receive a grade based on how many points you earned.

For example, if you did very well in your class and earned 980 points, you would earn a final course grade of an A. If you missed a few assignments and earned 800 points, you would earn a B and so on. In this system, it doesn't matter what someone else does, you are graded based upon whether you did the work and did it well or not. You are most likely familiar with standard grading.

Curved grading is different. Why? In a curved grading system, even if you earn 980 points out of 1,000, it doesn't necessarily mean you'll earn an A - it could mean you actually earn a B or even a C. Remember in our earlier example that only six students will be able to receive a grade of A and only six will get a B? How do you earn one of those grades?

Alright, here is where it gets complex. The most typical way to develop a curve system is to average all of the final grades. Perhaps, the average final grade is an 87%. This number now establishes the peak, or the top of the bell curve. Now, the 87% is actually a C instead of the regular B that you would expect. The instructor would go through all students' grades and assign them a final grade based on where they are placed on the new breakdown of percentages shown below, with 87% representing the C's. The following chart provides the breakdown of grades:

Breakdown of Grades
A = 96.75 - 100.00
B = 93.50 - 96.74
C = 6.51 - 93.49
D = 3.26 - 6.50
F = 0.00 - 3.25

If there are too many students in the A and B categories, they will get moved down one level based on where they are closest to on the new breakdown of grades. For example, if seven students scored in the B category, one of those students, the one closest to 93.49 points, would be moved down to the C category. While this doesn't seem fair, this practice balances out the distribution of scores.

To unlock this lesson you must be a Study.com Member.
Create your account

Register for a free trial

Are you a student or a teacher?
I am a teacher

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back

Earning College Credit

Did you know… We have over 95 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it free for 5 days!
Create An Account