The secret of income inequality in the US.

This first chart shows the relationship between income inequality and test performance on prose literacy. In the US, people who are bad at written and verbal communication skills are at a huge disadvantage. The second chart shows that in the US and China family plays the most important role in educational achievement and, as a consequence, in future earnings. 

Source: http://www.jstor.org/stable/27647039. The role of cognitive skills in economic development.