Curving student grades is done frequently in the U.S. educational system, especially in high school. Curving grades can ease stress on students because it takes into account the top ability in the class, making the results fair. If a test was so difficult that not even a well-performing student received a perfect score, then the entire class receives a break in the grading scale. However, in situations where someone did receive a perfect score, then grade curving won't help those who received lesser scores.

Calculate the difference between the total number of questions on the test and the total questions answered correctly by the top student. If your test had 25 questions and the top score was a 21, then there will be a difference of four points. Grading on a traditional bell curve may cause well-performing students to receive lower grades, which can be considered unfair. If all of your students perform well, it could mean very low grades for students who should have received a "B" or a "C."

Add the difference to each student's original score. The student who scored a 21 will now have a 25, taking them from an 84 percent to 100 percent. Students who had a score of 15 will now have a score of 19, taking their grade from a 60 percent to a 76 percent. Continue until you have calculated a new grade percentage for each student.

Turn the new grade percentages into letter grades. The top student, who would have earned a "B" before curving, will now receive an "A." Depending on the difference between the total number of questions on the test and the total questions answered correctly by the top student, several students may have grades that are a letter grade or more better than their original grade.