IQ tests, while hardly perfect, are useful predictors in a number of ways.
The tests are not statistically-biased predictors—i.e., blacks don't "overachieve" in the real world relative to their test scores. In colleges, in fact, they tend to underachieve on their grades relative to their SATs. (I have, however, argued at length, here and here, that because standardized tests can't measure improvisational ability, they miss an area where blacks tend to be strong.)
Over the last 85 years or so, blacks in America have averaged about one standard deviation lower on IQ tests than whites.
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