Willingham exhaustively catalogs the evidence (the article weighs in with 79 footnotes) for the parental investment and chronic stress theories to explain the academic performance differences between advantaged and disadvantaged students and notes that the theories are complementary. That is, both can explain the differences.
The first embodies the straightforward notion that families who can invest more in the education of their children, tend to do so, in a variety of ways: access to higher-quality healthcare, daycare, preschools and schools are just some examples. The second theory relates the chronic health, family and environmental stresses faced by disadvantaged children and the evidence that such long-term stress has effects emotionally, cognitively and physiologically on the make-up and chemistry of the brain.
Willingham's intent, as always, is to connect research to classroom practice. Instead of lowering expectations for disadvantaged children, classrooms should compensate for the stresses outside of school by presenting academically challenging material in calm and nurturing environments. He also notes the necessity of making other knowledge and skill goals more explicit, like how to interact with peers, adults, large institutions, and, authority figures; how to manage time; and, how to regulate one's emotions.
While believing that serious public action is needed - Willingham counsels teachers not to despair, asserting that all children can learn regardless of background.