Then they'd have to be very secretive about the contents of the exams. CTY takes this approach with its SCAT exam, and so do the people who make the Miller Analogies test. You can get enough information about each exam to understand the format of the test, but nothing else, really. They don't really release previous exams, and this cuts down A LOT on how much you can prep for these tests. I believe that it's generally agreed that you can't really prepare for an IQ test either (apart from learning tricks to remember number sequences?).
The standard IQ tests such as the WISC and Stanford-Binet exhibit large group differences, and the NAACP lawsuit is prompted by large group differences in admissions to NYC exam schools. So your suggestion above to use g-loaded tests that are difficult to prepare for -- effectively IQ tests -- would not solve the "problem".
