THE students at West Virginia University don't want you to think they take life too seriously. It is the third-best “party school” in America, according to the Princeton Review's annual ranking of such things, and comes a creditable fifth in the “lots of beer” category. Booze sometimes causes students' clothes to fall off. Those who wake up garmentless after a hook-up endure the “walk of shame”, trudging back to their own dormitories in an obviously borrowed football shirt, stirring up gossip with every step.

And yet, for all their protestations of wildness, the students are a serious-minded bunch. Yes, they have pre-marital sex. “I don't see how it's a bad thing,” says Ashley, an 18-year-old studying criminology. But they are careful not to fall pregnant. It would be “a major disaster,” says Ashley. She has plans. She wants to finish her degree, go to the FBI academy in Virginia and then start a career as a “profiler” helping to catch dangerous criminals. She wants to get married when she is about 24, and have children perhaps at 26. She thinks having children out of wedlock is not wrong, but unwise.

A few blocks away, in a soup kitchen attached to a church, another 18-year-old balances a baby on her knee. Laura has a less planned approach to parenthood. “It just happened,” she says. The father and she were “never really together”, merely “friends with benefits, I guess”. He is now gone. “I didn't want to put up with his stuff,” she says. “Drugs and stuff,” she adds, by way of explanation.

There is a widening gulf between how the best- and least-educated Americans approach marriage and child-rearing. Among the elite (excluding film stars), the nuclear family is holding up quite well. Only 4% of the children of mothers with college degrees are born out of wedlock. And the divorce rate among college-educated women has plummeted. Of those who first tied the knot between 1975 and 1979, 29% were divorced within ten years. Among those who first married between 1990 and 1994, only 16.5% were.

At the bottom of the education scale, the picture is reversed. Among high-school dropouts, the divorce rate rose from 38% for those who first married in 1975-79 to 46% for those who first married in 1990-94. Among those with a high school diploma but no college, it rose from 35% to 38%. And these figures are only part of the story. Many mothers avoid divorce by never marrying in the first place. The out-of-wedlock birth rate among women who drop out of high school is 15%. Among African-Americans, it is a staggering 67%.

Does this matter? Kay Hymowitz of the Manhattan Institute, a conservative think-tank, says it does. In her book “Marriage and Caste in America”, she argues that the “marriage gap” is the chief source of the country's notorious and widening inequality. Middle-class kids growing up with two biological parents are “socialised for success”. They do better in school, get better jobs and go on to create intact families of their own. Children of single parents or broken families do worse in school, get worse jobs and go on to have children out of wedlock. This makes it more likely that those born near the top or the bottom will stay where they started. America, argues Ms Hymowitz, is turning into “a nation of separate and unequal families”.

A large majority—92%—of children whose families make more than $75,000 a year live with two parents (including step-parents). At the bottom of the income scale—families earning less than $15,000—only 20% of children live with two parents. One might imagine that this gap arises simply because two breadwinners earn more than one. A single mother would have to be unusually talented and diligent to make as much as $75,000 while also raising children on her own. And it is impossible in America for two full-time, year-round workers to earn less than $15,000 between them, unless they are (illegally) paid less than the minimum wage.

But there is more to it than this. Marriage itself is “a wealth-generating institution”, according to Barbara Dafoe Whitehead and David Popenoe, who run the National Marriage Project at Rutgers University. Those who marry “till death do us part” end up, on average, four times richer than those who never marry. This is partly because marriage provides economies of scale—two can live more cheaply than one—and because the kind of people who make more money—those who work hard, plan for the future and have good interpersonal skills—are more likely to marry and stay married. But it is also because marriage affects the way people behave.

American men, once married, tend to take their responsibilities seriously. Avner Ahituv of the University of Haifa and Robert Lerman of the Urban Institute found that “entering marriage raises hours worked quickly and substantially.” Married men drink less, take fewer drugs and work harder, earning between 10% and 40% more than single men with similar schooling and job histories. And marriage encourages both spouses to save and invest more for the future. Each partner provides the other with a form of insurance against falling sick or losing a job.

Marriage also encourages the division of labour. Ms Dafoe Whitehead and Mr Popenoe put it like this: “Working as a couple, individuals can develop those skills in which they excel, leaving others to their partner.” Mum handles the tax returns while Dad fixes the car. Or vice versa. As Adam Smith observed two centuries ago, when you specialise, you get better at what you do, and you produce more.

Perhaps the most convincing work showing that marriage is more than just a piece of paper was done by Mr Lerman of the Urban Institute. In “Married and Unmarried Parenthood and Economic Wellbeing”, he addressed the “selection effect”—the question of whether married-couple families do better because of the kind of people who marry, or because of something about marriage itself.

Using data from a big annual survey, he looked at all the women who had become pregnant outside marriage. He estimated the likelihood that they would marry, using dozens of variables known to predict this, such as race, income and family background. He then found out whether they did in fact marry, and what followed.

His results were striking. Mothers who married ended up much better off than mothers with the same disadvantages who did not. So did their children. Among those in the bottom quartile of “propensity to marry”, those who married before the baby was six months old were only half as likely to be raising their children in poverty five years later as those who did not (33% to 60%).

Changes in family structure thus have a large impact on the economy. One of the most-cited measures of prosperity, household income, is misleading over time because household sizes have changed. In 1947, the average household contained 3.6 people. By 2006, that number had dwindled to 2.6. This partly reflects two happy facts: more young singles can afford to flee the nest and their parents are living longer after they go. But it also reflects the dismal trend towards family break-up. A study by Adam Thomas and Isabel Sawhill concluded that if the black family had not collapsed between 1960 and 1998, the black child-poverty rate would have been 28.4% rather than 45.6%. And if white families had stayed like they were in 1960, the white child poverty rate would have been 11.4% rather than 15.4%.

Children of the sexual revolution

Since the 1960s, the easy availability of reliable contraception has helped to spur a revolution in sexual mores. As opportunities for women opened up in the workplace, giving them an incentive to delay child-bearing, a little pill let them do just that without sacrificing sex. At the same time, better job opportunities for women changed the balance of power within marriage. Wives became less economically dependent on their husbands, so they found it easier to walk out of unhappy or abusive relationships.

As the sexual revolution gathered steam, the idea that a nuclear family was the only acceptable environment in which to raise a child crumbled. The social stigma around single motherhood, which was intense before the 1960s, has faded. But attitudes still vary by class.

College-educated women typically see single motherhood as a distant second-best to marriage. If they have babies out of wedlock, it is usually because they have not yet got round to marrying the man they are living with. Or because, finding themselves single and nearly 40, they decide they cannot wait for Mr Right and so seek a sperm donor. By contrast, many of America's least-educated women live in neighbourhoods where single motherhood is the norm. And when they have babies outside marriage, they are typically younger than their middle-class counterparts, in less stable relationships and less prepared for what will follow.

Consider the home life of Lisa Ballard, a 26-year-old single mother in Morgantown. She strains every nerve to give her children the best upbringing she can, while also looking for a job. Her four-year-old son Alex loves the Dr Seuss book “Green Eggs and Ham”, so she reads it to him, and once put green food colouring in his breakfast eggs, which delighted him. But the sheer complexity of her domestic arrangements makes life “very challenging”, she says.

She has four children by three different men. Two were planned, two were not. Two live with her; she has shared custody of one and no custody of another. One of the fathers was “a butthole” who hit her, she says, and is no longer around. The other two are “good fathers”, in that they have steady jobs, pay maintenance, make their children laugh and do not spank them. But none of them still lives with her.

Miss Ballard now thinks that having children before getting married was “not a good idea”. She says she would like to get married some day, though she finds the idea of long-term commitment scary. “You've got to definitely make sure it's the person you want to grow old with. You know, sitting on rocking chairs giggling at the comics. I want to find the right one. I ask God: ‘What does he look like? Can you give me a little hint?'”

If she does find and wed the man of her dreams, Miss Ballard will encounter a problem. She has never seen her own father. Having never observed a stable marriage close-up, she will have to guess how to make one work. By contrast, Ashley, the criminology student at the nearby university, has never seen a divorce in her family. This makes it much more likely that, when the time is right, she will get married and stay that way. And that, in turn, makes it more likely that her children will follow her to college.

Most children in single-parent homes “grow up without serious problems”, writes Mary Parke of the Centre for Law and Social Policy, a think-tank in Washington, DC. But they are more than five times as likely to be poor as those who live with two biological parents (26% against 5%). Children who do not live with both biological parents are also roughly twice as likely to drop out of high school and to have behavioural or psychological problems. Even after controlling for race, family background and IQ, children of single mothers do worse in school than children of married parents, says Ms Hymowitz.

Children whose father was never around face the toughest problems. For those whose parents split up, the picture is more nuanced. If parents detest each other and quarrel bitterly, their kids may actually benefit from a divorce. Paul Amato of Penn State University has found that 40% of American divorces leave the children better (or at least, no worse) off than the turbulent marriages that preceded them. In other cases, however, what is good for the parents may well harm the children. And two parents are likely to be better at child-rearing because they can devote more time and energy to it than one can.

Research also suggests that middle- and working-class parents approach child-rearing in different ways. Professional parents shuttle their kids from choir practice to baseball camp and check that they are doing their homework. They also talk to them more. One study found that a college professor's kids hear an average of 2,150 words per hour in the first years of life. Working-class children hear 1,250 and those in welfare families only 620.

Co-habiting couples have the same number of hands as married couples, so they ought to make equally good parents. Many do, but on average the children of co-habiting couples do worse by nearly every measure. One reason is that such relationships are less stable than marriages. In America, they last about two years on average. About half end in marriage. But those who live together before marriage are more likely to divorce.

Many people will find this surprising. A survey of teenagers by the University of Michigan found that 64% of boys and 57% of girls agreed that “it is usually a good idea for a couple to live together before getting married in order to find out whether they really get along.” Research suggests otherwise. Two-thirds of American children born to co-habiting parents who later marry will see their parents split up by the time they are ten. Those born within wedlock face only half that risk.

The likeliest explanation is inertia, says Scott Stanley of the Centre for Marital and Family Studies at the University of Denver, Colorado. Couples start living together because it is more fun (and cheaper) than living apart. One partner may see this as a prelude to marriage. The other—usually the man—may see it as something more temporary. Since no explicit commitment is made, it is easier to drift into living together than it is to drift into a marriage. But once a couple is living together, it is harder to split up than if they were merely dating. So “many of these men end up married to women they would not have married if they hadn't been living together,” says Mr Stanley, co-author of a paper called “Sliding versus deciding”.

A little help from the government

Most American politicians say they support marriage, but few do much about it, except perhaps to sound off about the illusory threat to it from gays. The public are divided. Few want to go back to the attitudes or divorce laws of the 1950s. But many at both ends of the political spectrum lament the fragility of American families and would change, at least, the way the tax code penalises many couples who marry. And some politicians want the state to draw attention to benefits of marriage, as it does to the perils of smoking. George Bush is one.

Since last year, his administration has been handing out grants to promote healthy marriages. This is a less preachy enterprise than you might expect. Sidonie Squier, the bureaucrat in charge, does not argue that divorce is wrong: “If you're being abused, you should get out.” Nor does she think the government should take a view on whether people should have pre-marital sex.

Her budget for boosting marriage is tiny: $100m a year, or about what the Defence Department spends every two hours. Some of it funds research into what makes a relationship work well and whether outsiders can help. Most of the rest goes to groups that try to help couples get along better, some of which are religiously-inspired. The first 124 grants were disbursed only last September, so it is too early to say whether any of this will work. But certain approaches look hopeful.

One is “marriage education”. This is not the same as marriage therapy or counselling. Rather than waiting till a couple is in trouble and then having them sit down with a specialist to catalogue each other's faults, the administration favours offering relationship tips to large classes.

The army already does this. About 35,000 soldiers this year will get a 12-hour course on how to communicate better with their partners, and how to resolve disputes without throwing plates. It costs about $300 per family. Given that it costs $50,000 to recruit and train a rifleman, and that marital problems are a big reason why soldiers quit, you don't have to save many marriages for this to be cost-effective, says Peter Frederich, the chaplain in charge.

Several studies have shown that such courses do indeed help couples communicate better and quarrel less bitterly. As to whether they prevent divorce, a meta-analysis by Jason Carroll and William Doherty concluded that the jury was still out. The National Institutes of Health is paying for a five-year study of Mr Frederich's soldiers to shed further light on the issue.

Americans expect a lot from marriage. Whereas most Italians say the main purpose of marriage is to have children, 70% of Americans think it is something else. They want their spouse to make them happy. Some go further and assume that if they are not happy, it must be because they picked the wrong person. Sometimes that is true, sometimes not. There is no such thing as a perfectly compatible couple, argues Diane Sollee, director of smartmarriages.com, a pro-marriage group. Every couple has disputes, she says. What matters most is how they resolve them.

At the end of the day, says Ms Squier, the government's influence over the culture of marriage will be marginal. Messages from movies, peers and parents matter far more. But she does not see why, for example, the government's only contact with an unmarried father should be to demand that he pay child support. By not even mentioning marriage, the state is implying that no one expects him to stick around. Is that a helpful message?