Marriage: Reason for Expanding Education Gap?

I just read an article from The New York Times called 'Education Gap Grows Between Rich and Poor, Studies Say' expecting to write a blog post on social class, but instead I am finding myself more interested in the idea the article expresses of marriage being a primary reason the gap keeps expanding.

Marriage has to do with the increasing education gap in two ways. The first is "the tendency of educated people to marry other educated people" (NYT). The studies in this article show that wealthier people are more educated than poor people; therefore to say educated people marry other educated people is to say that wealthy people marry other wealthy people, thus containing wealth in a small circle (for more on that idea, check out a previous blog post I wrote called 'The Circle of the Wealthy'). Poor people now have no way of breaking into the circle because they aren't part of that crowd.

The second connection between marriage, or lack of marriage, and the increasing education gap is the fact that lower income families "are now more likely than ever to be headed by a single parent" (NYT). The state of the single parent could be divorce or no marriage in the first place, but it all basically means the same thing. Single-parent households bring in less money than households with married parents. Consequently, single-parent households have less money to spend on education for their children, which adds to the gap.

So my question is this: how are single-parent households, where their status may or may not be their choice, expected to compare to households with a combination of two incomes?