Psychometricians will hate this answer (they think IQ measure general intelligence), but I contend that IQ tests measure academic skills and knowledge. When you look at the items on the Stanford-Binet or the WAIS, you see items that require knowledge typically gained in school: math, vocabulary, logical reasoning, even geography. In short, if you want to know who will succeed in academic settings, give the person an IQ test.
--Now, let me rush to add there are many, many valuable types of intelligence that are not assessed by an IQ test! Psychological research by cognitive psychologists like Sternberg and Ceci clearly demonstrates that people are capable of intelligent behavior that is not accurately measured by an IQ test.
Miles