IQ graphics,
http://library.flawlesslogic.com/iq.htm
http://www.lagriffedulion.f2s.com/sft.htm
Search Google for Graph of Black IQ and there are many other charts that support the general thesis.
The links above are but two items that discuss this in more detail.. I have been excoriated previously for bringing this matter up in this fashion. It doesn’t make it any less true.
The reality is that overall, the culture of American blacks does not generate an overall improvement in IQ scores.
The latter article implies genetics, but I don’t believe that is reasonable. It is a matter of culture in those areas where the IQ scores are lowest.