An article in the Atlantic discusses the growing phenomenon of American students studying and succeeding in a wide variety of advanced mathematics courses and competitions. This includes organizations like MathCounts (which I coached at the JHS level for many years) as well as special summer math programs like MathPath, as well as math circles and AP calculus and statistics courses.
However, as the author notes:
National achievement data reflect this access gap in math instruction [between US poor kids and US rich kids – gfb] all too clearly. The ratio of rich math whizzes to poor ones is 3 to 1 in South Korea and 3.7 to 1 in Canada, to take two representative developed countries. In the U.S., it is 8 to 1. And while the proportion of American students scoring at advanced levels in math is rising, those gains are almost entirely limited to the children of the highly educated, and largely exclude the children of the poor. By the end of high school, the percentage of low-income advanced-math learners rounds to zero.