What does 'on the curve' mean?

Solution 1:

StoneyB is right about the origin of the phrase "on the curve." It comes from assigning letter grades ABCDF based on the (assumed) normal distribution of students' numerical scores instead of on a linear scale of A=90-100, B=80-90, C=70-80, etc. It has come to mean adjusting the grading to boost lower scores that would have been failing under a linear system into the passing range (although that isn't what necessarily what would happen in the mathematical sense of the term).

The quote means that under previous, supposedly more rigorous, considerations of Presidential candidates, W wouldn't have been elected President, but under the easier "curved grading," was given passing marks that made him electable.

Perhaps an example would help. Suppose that the average grade of C on a test is pegged to 70% correct answers, and the test is very difficult. The average score comes in at 50, but that's a failing grade on the linear scale. The class will beg the teacher to grade on a curve, making 50 a C.