Grading on a Curve

The discussion of z-scores and centering may have reminded you of something we are all familiar with from our school days: grading on a curve. When teachers grade on a curve, they are doing something very similar to what we described in our summaries of z-scores and centering.

They first calculate the average scores and the standard deviation for the class. Then, instead of assigning grades based on your absolute score (e.g., 90+ = A, 80-89 = B), they assign grades based on how many standard deviations a score is from the mean (e.g., scores within one standard deviation above the mean get a B, two standard deviations above get an A, one standard deviation below the mean gets a C, etc.).