According to this article from the BBC, http://www.bbc.co.uk/news/magazine-22025328:
As many as 15% of white students admitted to elite colleges don't meet admissions standards.
This quote seems to be a rephrasing of a quote from this article (that the above article links to):
Researchers with access to closely guarded college admissions data have found that, on the whole, about 15 percent of freshmen enrolled at America's highly selective colleges are white teens who failed to meet their institutions' minimum admissions standards.
This number is hard for me to believe, and I wonder if this claim has any basis.