After Hurricane Katrina struck New Orleans and introduced the public to the horrific sight of those desperate people in the Superdome, Newsweek headlined its coverage of the event “The Other America.” The phrase was an allusion to the 1962 book by Michael Harrington that helped inspire the War on Poverty and perhaps also to John Edwards’s “Two Americas,” a book about American haves and have-nots that received far too much fawning attention during Mr. Edwards’s vice-presidential run. Kay Hymowitz, a fellow at the Manhattan Institute, freely admits that there are two Americas. But that is where the resemblance to Mr. Edwards’s and Mr. Harrington’s analysis ends.

For Ms. Hymowitz, the two Americas do not divide between the poor who are supposedly in need of government assistance and the rest of us. The division is best defined in another way: between those who see marriage as an indispensable condition of child-rearing and those who don’t. If we are becoming two Americas, it is one America in which parents are married and another in which they are not. The Marriage Gap, as Ms. Hymowitz calls it, appears likely to have a more profound effect on the future of both Americas than the gender gap so lamented by the feminists.

Despite the “unmarriage revolution” ushered in by the noxious 1960s, the anti-civilization decade, marriage is again flourishing among well-educated women. Today’s educated mothers may work outside the home or not, but they and their husbands are committed to what Ms. Hymowitz calls The Mission — the project of shaping their children into adults (and citizens) who have the requisite skills and self-discipline to prosper in a complex, postindustrialist society.

The Mission, notes Ms. Hymowitz, requires not a village but two married parents. And, no, cohabitation doesn’t do the trick. Even cohabiters who have the education levels of their married counterparts are less effective as parents. “As the core cultural institution,” Ms. Hymowitz writes, “marriage orders life in ways that we only dimly understand. It carries with it signals about how we should live, signals that are in line with both our economy and our politics in the largest sense.”

While there is more marriage among the better educated, with 92% of children living with two parents coming from families that have an income of $75,000 or better, there is less marriage among inner-city parents. “Only about 20 percent of kids in families earning under $15,000 live with both parents,” writes Ms. Hymowitz. Which raises a question: “Why would women working for a pittance at supermarket cash registers decide to have children without getting married while women writing briefs at Debevoise & Plimpton, who could easily afford to go it alone, insist on finding husbands before they start families?”

The answer, in Ms. Hymowitz’s view, is that many among the urban poor have lost the “life script” for future-oriented child-rearing. Policy makers may assume that the problem is a shortage of employed, marriageable men. But the problem is more existential, a loss of a sense that marriage and children are connected.

The most fascinating (but grimmest) sections of “Marriage and Caste in America” deal with child-rearing skills in the unmarried America. Children of single mothers on welfare, for instance, hear their mother use fewer words. (According to one study cited in the book, the average words heard per hour are 2,150 for a professor’s children, 1,250 for working-class children and 620 for children in welfare families.) What is more, the talk of the welfare parents in the study “was meaner and more distracted.” It is not that these parents don’t love their children; it is that they do not have a “script” for being parents. Thus they find it particularly difficult to rear children capable of thriving in a knowledge-based society.

According to Ms. Hymowitz — and this is the scariest part of the book — most social analysts ignore the root of the problem and therefore end up prescribing “solutions” that actually “smooth the way” for single parenthood. “To listen to some policymakers,” she writes, “one might think that wanting to become a lawyer or anchorwoman — and possessing the requisite orderliness, discipline, foresight, and bourgeois willingness to delay gratification — are natural instincts rather than traits developed over time through adults’ prodding and example.”

Optimism is always more appealing than pessimism, and Ms. Hymowitz tries to be hopeful, proclaiming a renewed stature for marriage — in the culture at large — as the key institution in child-rearing. She may be right about middle-class parents, but it is not clear whether the message has yet reached unmarried America. If policy makers heed the arguments and analysis in “Marriage and Caste in America,” then Ms. Hymowitz’s optimism will at least be partly justified.

For myself, I feel certain that the next time one of my friends can’t meet me for lunch because she is ferrying her offspring to yet another life-enhancing lesson, I won’t be annoyed. I’ll know that she is nobly engaged in The Mission, important not just to the edification and college-admission forms of her offspring but also to the health of the republic. It is a Mission, too, that she can best perform with a man who is her husband.

Ms. Hays is senior editor at the Independent Women’s Forum.