Grading on a curve adjusts scores based on class performance, often by shifting scores so the highest grade becomes 100 or matching a set distribution.
How it works
- Instructor takes the highest score.
- Shifts everyone’s score up so the top becomes 100%.
- Or scales grades to a set distribution, such as 10% A, 20% B, 40% C.
Example
If the top score is 88, add 12 points to each score.
Pros and cons
Helps when a test is too hard. Can reduce rewards for high performance.
Other
A bell curve distribution uses mean and standard deviation.
Meaning of curve
In education, “curving” means adjusting grades based on the class results. There are several methods and none is universal.
Common methods
- Add points: raise everyone’s score by the same amount so that the top score becomes 100.
- Percent scaling: multiply scores by a factor.
- Square root curve: new score = 10 times the square root of the original score, which helps lower scores more.
- Bell curve (normal distribution): assign grades based on standard deviations from the mean, so the average score becomes a C and a fixed percentage gets each letter grade.
Example
If the top score on an exam is 92 and the instructor adds 8 points to everyone, a 70 becomes 78. With a square root curve, 64 becomes 80 and 81 becomes 90.
Grading on a distribution
A typical distribution might be 10% As, 20% Bs, 40% Cs, 20% Ds and 10% Fs. This method makes grades relative to other students and may create competition.
Pros
- Corrects tests that were too hard.
- Maintains consistent grade distribution across sections.
Cons
- Students can be hurt when classmates perform well.
- Reduces the link between grades and mastery of material.
- Many educators prefer criterion referenced grading, where grades reflect set standards.
Use in practice
Some law schools and large science courses use fixed curves, while many high schools and colleges do not curve at all.
Ask
Check the syllabus, because instructors must state their grading policy.
Methods of curving
Grading on a curve adjusts scores based on class performance. One simple method adds points to every score so that the top score becomes 100, for example adding 8 points if the highest score is 92. Another scales scores proportionally. A strict normal curve assigns grades by percentile or z-score, for example giving A to the top 10 to 15 percent, which makes grades relative to classmates. Different instructors use different methods, and many do not curve at all.
Pros, cons and practice
A curve can offset an overly hard test and keep grades fair across sections, but a rank based curve forces some students to receive low grades even if everyone learned the material, and it can discourage collaboration. Curving after the fact is more common in large science and law classes. Check the syllabus for the grading policy and ask the instructor if you are unsure. Even with a curve, your best strategy is to study consistently and aim to master the content.
Based on data from university teaching and learning centers
