The third prong is a bit badly posed: descriptively, white kids test better than black kids, and each of the three prongs offers an explanation. The third prong points to a discredited belief of genetic inferiority; by positioning the three prongs as exhaustive, the author structures the argument such that if you don't accept either of the first two prongs, then you must be a racist.

Perhaps. I didn’t really read that much into GGP’s comment. I just wanted to point out that the comment does (minimally) rebut scientific racism. And by selectively omitting that rebuttal in the quote, GP makes it appear as if the denial of scientific racism is just a claim of faith.