The black-white test score gap does not appear to be an inevitable fact of nature. It is true that the gap shrinks only a little when black and white children attend the same schools. It is also true that the gap shrinks only a little when black and white families have the same amount of schooling, the same income, and the same wealth. But despite endless speculation, no one has found genetic evidence indicating that blacks have less innate intellectual ability than whites. Thus while it is clear that eliminating the test score gap would require enormous effort by both blacks and whites and would probably take more than one generation, we believe it can be done.
This conviction rests mainly on three facts:
--When black or mixed-race children are raised in white rather than black homes, their preadolescent test scores rise dramatically. Black adoptees' scores seem to fall in adolescence, but this is what we would expect if, as seems likely, their social and cultural environment comes to resemble that of other black adolescents and becomes less like that of the average white adolescent.
--Even nonverbal IQ scores are sensitive to environmental change. Scores on nonverbal IQ tests have risen dramatically throughout the world since the 1930s. The average white scored higher on the Stanford-Binet in 1978 than 82 percent of whites who took the test in 1932. Such findings reinforce the implications of adoption studies: large environmental changes can have a large impact on test performance.
--Black-white differences in academic achievement have also narrowed throughout the twentieth century. The best trend data come from the National Assessment of Educational Progress (NAEP), which has been testing seventeen-year-olds since 1971 and has repeated many of the same items year after year. Figure 1-2 shows that the black-white reading gap narrowed from 1.25 standard deviations in 1971 to 0.69 standard deviations in 1996. The math gap fell from 1.33 to 0.89 standard deviations. When Min-Hsiung Huang and Robert Hauser analyzed vocabulary scores for adults born between 1909 and 1969, the black-white gap also narrowed by half.