They’ve used a variety of what are called IQ tests, both individually administered and pencil and paper tests. There is no question, the inner city kids and those without an intact family don’t get the exposure to language from an early age.
Researchers have actually tape recorded verbal interaction in homes and looked at the number of different words the kids are exposed to on average in a day. In some families children are exposed to hundreds of different words. In other famiies there is very little verbal interaction. The children with the rich verbal environment do much better on IQ tests. On average. Programs like Headstart can’t seem to make up for the lack of parental verbal interaction.
It makes sense. If a child is not exposed to words, or if they’re not exposed to concepts like less/more, over/under, good/bad, big/small, sweet/sour - they’re not going to do well in school when other children are being taught letters and numbers at the age of two or younger.
My original comment, regarding how to save these children, was to have them adopted as infants, by Christian home-schoolers.
I also said I don't buy the conclusion that blacks are less intelligent, and that the underlying difference was cultural.
Reflecting on what you just stated...I don't think I was wrong.