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How to Use a Bell Curve to Assign Grades

A bell curve is a grading curve that represents the number of students that obtained each score. When most students score somewhere in the middle, the graph of students scores forms a bell shape. Grading on a bell curve is one way to ensure that students' grades are adjusted relative to the fairness of the test and quality of instruction. When most students fail a test, for example, there may have been a problem with the test itself, so the grades are curved in order to be fair. There are several different ways to grade on a bell curve.

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Instructions

- 1
  Determine the highest grade in the class. If the highest grade is within 7 to 8 points of the next-highest grade, subtract the highest grade from 100. Add the difference between the two numbers to each student's grade. If, for example, the highest grade is an 80, the difference between this number and 100 is 20. Therefore, add 20 points to each student's grade.
- 2
  Curve the scores based on the lowest grade if the highest grade is substantially higher than the next-highest grade. Determine what you would like for the lowest grade on the test to be. Then deduct the lowest grade received from the ideal lowest grade. Add the difference between the two numbers to every student's grade. For example, if the lowest grade is a 30 and you would like for the lowest grade to be a 55, add 25 points to each student's grade.
- 3
  Use the middle scores to determine the grading curve if you'd prefer not to focus on the highest and lowest scores. Determine the average score by adding up all of the scores, then dividing by the total number of test takers. Then determine what you would like for the average score to be and add this number to each student's grade. If the average score was a 55 and you would like the average score to be a 70, then add 15 points to each student's grade.

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