I wish I could tell you that your observations were wrong. They aren't. It is largely a matter of class, not race. Those in the upper classes have access to the resources that help them succeed, including family members who have the skill and social capital to push AP and accelerated classes. At the same time, in this country we do not have equal access to the upper classes in all races. You are right that suburban school districts often have fewer minorities in advanced classes. They have fewer minorities in middle and upper classes.
I found this article from The Journal of Blacks in Higher Education interesting.
As the article notes, there has been an increase in the number of black students in AP classes, but there is still a disparity in the success rate of different students.
Traditionally, most participants in the AP program have been concentrated in the high schools in affluent, predominantly white suburbs of major cities. Also, in many racially integrated high schools, large numbers of black students have not been sufficiently prepared to take on the AP curriculum. (para 9)
If the students do not have access to the same preparation, and the same support system, they cannot be as successful. This is where we need to focus our efforts. Black children are just as smart as others. The schools they attend and the neighborhoods they live in are often barriers to their success.
As a country, we need to stop accepting the status quo. It cannot be all right to siphon poor children in the ghettos into gangs and prisons, instead of colleges.
For more, read here: http://www.jbhe.com/features/59_apscoringgap.html
And here: http://professionals.collegeboard.com/data-reports-research/ap/nation
Citation: "More Blacks Are Competing in Advanced Placement Programs, But the Racial Scoring Gap Is Widening." More Blacks Are Competing in Advanced Placement Programs, But the Racial Scoring Gap Is Widening. Journal of Blacks in Higher Education. Web. 07 May 2012. <http://www.jbhe.com/features/59_apscoringgap.html>.