“Doesn’t this mean that the system is failing African American students and that they are falling farther behind?” To her evident annoyance, I told her that I had no idea and that I would need different data to answer her question. The problem, I explained to her, is that when performance is reported in terms of standards, comparisons of trends in performance between two groups that start out at different levels—such as whites and African Americans in Boston—are almost always misleading. There are two different statistics used for this purpose. One is the statistic she used: the composition of
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