An good essay on marriage: Kay Hymnowitz's Marriage and Caste in America, a paper given at the Heritage Foundation. she discusses what she calls "the marriage gap":
We are becoming a nation of separate and unequal families that threatens to last into the foreseeable future. On the one hand, well-educated women make more money. They get married, only then have their children, and raise them with their husbands. Those children are more likely to grow up to be well-adjusted, to do well in school, to go to college, to marry and only then have children.
On the other hand, we have low-income women raising children alone who are more likely to be low-income, to drop out of school or, if they do make it to college, go to a less elite college, and to become single parents themselves.