This is true. Various studies have been done which measure how much of college GPA and other such things can be predicted based on academic inputs.
http://ftp.iza.org/dp8733.pdf
http://www.mindingthecampus.org/2010/09/the_underperformance...
It turns out that "underprivileged" people actually do worse than what IQ and other academic measurements alone would predict.
If universities actually wanted to accurately choose the students most likely to succeed, they would penalize blacks, hispanics, males and people with low family income.
Second, IQ and race is a highly studied area and the differences are likely to do with many of the exact same factors that lead to socioeconomic inequality between the races.
If this is true, you should be able to run a multiple regression analysis which takes into account those "exact same factors" as well as race, and which accurately predicts outcomes. Further, the coefficient on race should be close to zero.
(This is the exact opposite of what is found in the studies I link above.)
Can you cite a study demonstrating this?