Hong Kong and Singapore's schools are great because they are full of Chinese, in the same way that schools with many Chinese in the US do very well, even in poor neighborhoods:
http://articles.latimes.com/2008/jul/16/local/me-lincoln16
To begin with, the eight students agreed on a few
generalities: Latino and Asian students came mostly from
poor and working-class families.
According to a study of census data, 84% of the Asian and
Latino families in the neighborhoods around Lincoln High
have median annual household incomes below $50,000. And
yet the Science Bowl team is 90% Asian, as is the Academic
Decathlon team.
It is thus not likely to be the schools. It is more likely to be culture or (more controversially) genetics. But most articles don't even consider such explanations, preferring to keep looking under the streetlight for that quarter.