Check out Charles Murray’s article on No Child Left Behind, which details the folly of using pass percentages, rather than mean scores, to determine changes in achievement gaps.

Warning: Murray’s story about the English teacher who quit because of standardized testing is lame, and his mention of the Harvard Civil Rights Project report is distracting. Ignore these paragraphs and concentrate on the test scores.

Indeed, Murray is at his best when explaining how changes in the gap (normally distributed) are contingent on the score required to be “proficient.” He also alludes to the fact that, when using pass percentages, an increase in scores over all groups will shrink group-to-group differences.

The point, according to Murray, is that, “All the children cannot be above average.” Of course, this flies right in the face of No Child Left Behind.