Grading on a curve
Grading on a curve means adjusting student scores according to how the whole class performed, instead of grading each student against a fixed standard. The curve can add points for everyone, or rank students and hand out grades in fixed shares. It usually helps when a test came out harder than planned, but it is the instructor's choice, never a right.
In more detail
The word curve points to the bell curve, but most curving in practice is simpler: the instructor shifts scores up. Only a strict bell curve forces grades into fixed shares, for example the top 10 percent get an A and the bottom 10 percent fail, whatever the raw scores were. That is also the one version where your grade depends on your classmates: a good raw score can still land a lower grade if the whole class did well.
Curving is a norm-referenced approach, because your result is read against other students. The alternative is a criterion-referenced approach, where you pass by meeting a fixed standard no matter how others did. When someone says a course is curved, ask which one is meant. "We add points if the average is low" and "only 20 percent get an A" are very different deals.
Curving is most common in large courses where a single exam is hard to calibrate. A ranked bell curve needs a big class to make sense, because with a few students one outlier moves the whole curve. Many instructors skip it entirely and simply adjust the grade boundaries or drop a badly written question.
Four common ways to curve (top score 88, class average 62)
| Method | How it works | A raw 64 becomes |
|---|---|---|
| Flat boost to the top score | Add 100 minus the top score to everyone | 76 (+12) |
| Square root | 10 times the square root of your score | 80 |
| Shift to a target average | Add the same points to everyone until the average hits the target, here 62 to 75 means +13 | 77 |
| Bell curve by rank | Grades handed out by rank in fixed shares | Depends on your rank, not the number |
Example
In a chemistry midterm the highest score is 88 out of 100 and the class average is 62. The instructor adds 12 points to everyone so the top score becomes 100. Ana had 64 and ends up at 76. Ben had 50 and ends up at 62, which clears a pass line of 60 that he would have missed. The gap between students stays the same, but everyone moves up by the same amount.
How to use it
- 1
Find out from the syllabus or the instructor whether a curve is used at all and which kind.
- 2
Never plan around a curve. Study as if the raw score has to reach the grade you want.
- 3
After each test, ask for the class average and the top score. They show how big a curve to expect.
- 4
Track where you stand by concept, not only by total score, so you know which topics cost you points.
- 5
Keep a margin. A raw score right at the cutoff leaves nothing for a curve that never comes.
How StudyPDF does this
StudyPDF measures you against your material, not against classmates. Every quiz and exam answer feeds a mastery score per concept, so you see what you actually know whether or not a curve is applied. Practice exams are sectioned and optionally timed like the real thing, with a graded report per section. That gives you a raw score to plan around instead of hoping for a curve.
See also
Put it to work on your own course
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Common questions
How do you grade on a curve?
The simplest way is to add the same number of points to everyone so that the top score becomes 100. Other ways are adding points until the class average reaches a target, or taking 10 times the square root of each score. A strict bell curve ranks students and gives out fixed shares of each grade.
Is grading on a curve good or bad for students?
It depends on the method. Adding points helps nearly everyone and protects against an unfairly hard test. A ranked bell curve makes your grade depend on classmates, which can lower a good raw score and push students to compete instead of sharing notes.