I'm not sure that looking at the tails of the curve is the most meaningful place to look.
the Armed Forces gives everyone an IQ-type test. they also test proficiency in many areas. there is a direct positive relationship between intelligence and performance. the AF has a cuttoff of about IQ90 which disqualifies more than half of blacks and about a third of whites. thats why there are less racial disparities in the Armed Forces, they are prescreened for intelligence. once on purpose in the Vietnam era and once accidentally in the 90's, recruits were let in under the cutoff with dismal results. the proficiency testing in many areas has been especially useful because it has been broken down into such small and basic components that it is a simple pass/fail mark rather than a supervisor's opinion. this has taken racism out of the testing but not racial disparity out of the results. simply put- the average black IQ tends to bunch up in the low-to-mid 90's and the white IQ tends to bunch up around 105. and whites end up with more technologically difficult jobs and higher proficiency rankings.
I was trying to compare blacks from different cultures to blacks in the US in order to look at the potential for blacks as a race. I dont think that black culture in the US is rewarding academic acheivers as other black cultures do elsewhere around the world.
Dont know why that is, but for the last twenty years I have heard one anecdotal story after another of smart young blacks hiding their intelligence by underperforming, or getting beat up for 'acting white' because they did well in school, etc. Then their is this whole bad boy rap image thing that is pushed on blacks by entertainment media.
Not being an American black, I can only guess about what the influences might be, but seeing how well blacks do in other countries that dont suffer from the situation here suggests that there are other factors than merely racial genetics.
try googling Ogbu's research on Shaker Heights. it discusses a bunch of aspects on why blacks underachieve academically