I don't have the statistics to prove it but I think there is one group that consistently made the transition from lower social economic class to higher in just one or two generations: Immigrants, irregardless of their origin. All you have to do is visit Miami, LA, SF, Orange Cty... and see for yourself the vibrant economies of the immigrant communities. Many of them came broke and uneducated.
immigration is a self-selection process... the most hard working / risk-taking portion of the population are more likely to uproot from their home country, go to a foreign land and try to create a better life than they otherwise would have if stayed home.