Does the stress of poverty cause the "acheivement gap"?

In a study published this week in the Proceedings of the National Academy of Sciences, scientists from Cornell University found that the reduced capacity of the working memories of the poor is almost certainly the result of stress affecting the way that brains develop during childhood. In other words, the chronic stress of long-term poverty seems to be responsible for the "achievement gap" that contributes to poverty passing from one generation to the next. This article in this week's Economist refers to the Marmot studies and notes, "The main reason poor people are stressed is that they are at the bottom of the social heap as well as the financial one... So, it may not be necessary to look any further than their place in the pecking order to explain what Dr Evans and Dr Schamberg have discovered in their research into the children of the poor." (Yes, the Economist actually printed that!) The study authors showed that the relationship between childhood poverty and reduced working memory was mediated through chronic stress in childhood, measured through "allostatic load" -- a "biological marker of cumulative wear and tear on the body that is caused by the mobilization of multiple physiological systems in response to chronic environmental demands." If you're up for it, you can find the full text of the original research article here.