Teachers: curve a test fairly and see the new grades.
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Curving adjusts scores when a test turned out harder than intended. The simplest methods scale everyone so the top score becomes 100%, or add the same points to every score.
The square-root curve (√score × 10) lifts low scores more than high ones, and the bell curve rescales the class to a chosen average and spread. Scores are capped at the maximum.
| Scores | 55, 62, 70, 78, 85, 88 |
| Curve method | Highest score becomes the target |
| Target top score | 100 |
| Maximum possible score | 100 |
| Target mean (bell curve) | 75 |
| Target standard deviation (bell curve) | 10 |
| New class average | 83 (was 73) |
| Method | Highest score becomes 100 |
| Highest / lowest | 100 / 62.5 |
| Original standard deviation | 13.02 |
83 (was 73).
| Scores | 45, 60, 64, 72, 81 |
| Curve method | Square-root curve |
| Target top score | 100 |
| Maximum possible score | 100 |
| Target mean (bell curve) | 75 |
| Target standard deviation (bell curve) | 10 |
| New class average | 79.9 (was 64.4) |
| Method | Square-root curve |
| Highest / lowest | 90 / 67.1 |
| Original standard deviation | 13.5 |
79.9 (was 64.4).
Pick a method: scale so the top score is 100, add flat points, use the square-root curve, or rescale to a target mean and standard deviation.
New score = √(old score) × 10 on a 100-point test; 64 becomes 80.
It corrects for a test that was too hard, but a bell curve can force some students into lower grades regardless of mastery.
No — all these methods keep students in the same order.