Every year at Gloucester High School in Massachusetts, three or four girls get pregnant. But not this year. This year 17 did. When Time magazine alleged that some of the girls had a “pregnancy pact”, reporters and cameramen from around the world descended on the fishing port. Whether the pact was a teenage dare or a practical arrangement by the girls to give each other moral support has been hotly debated. No one disputes, though, that many were delighted to discover they were pregnant. “Sweet!” one of them shouted in the school nurse’s office. The school superintendent admitted: “They were not trying very hard not to get pregnant.”

“Every child a wanted child” was the old slogan of the movement for birth control. But it is part of the folklore of feminism that no teenager ever wants a child. “Profoundly shocking,” wrote the Gloucester Daily Times. “The idea of 15- and 16-year-old girls wanting to become pregnant, wanting to make such a life-altering choice so early in their lives – and others being ‘disappointed’, not relieved, when learning their pregnancy tests proved negative – is a notion that seems absolutely contrary to most of our psyches.” This is untrue. Having babies at 16 is perfectly in line with our psyches, as a look at other cultures and our own history shows. What it is contrary to is our ideology. Pact or no, the Gloucester pregnancies are some kind of a rebellion.

Any talk-radio blowhard can find evidence that Gloucester High was either too lax or too stern. Massachusetts is the most sexually libertarian of the 50 United States – it was the first to allow gay marriage and gives wide latitude to cities and towns in the sex-counselling services they provide students. Yet Gloucester is a church-dominated Portuguese-, Italian- and Irish-American city. So its sex education is a mix of traditional and non-judgmental programmes. The school does not hand out condoms but has a crèche for teen mothers. Since Gloucester is a largely white city, commentators can give vent to all sorts of snorting stereotypes about pregnant teenagers, their parents and their culture, without fear of being called racist.

Like every debate over teen pregnancy, this one is a duel of dogmas. On one side is the view that chastity is a moral absolute. The chairman of the school board has suggested prosecuting the girls’ boyfriends for statutory rape. On the other side is the view that, where birth control is available, girls forgo it only out of either ignorance or shame. This is the view of most news media and of Gloucester’s mayor, who blamed her town’s pregnancies on George W. Bush. His No Child Left Behind programme diverted to academics money that should have been spent on sex education, which is now taught only until age 15.

At the risk of sounding crude, though, the parts of sex education relevant to preventing teen pregnancy can be taught in five minutes. It may flatter our self-regard to believe that the modern, western pattern of child-bearing arises from superior knowledge and sophistication, but it does not. It arises from our priorities. The Gloucester pregnancies are not about information the girls don’t have. They are about an argument the girls don’t buy. It is a fool’s errand to try to convince a girl that bearing a child is “sad” (a word used with appalling frequency in press accounts) or to argue that last year’s hit movie Juno leads girls astray by glamorising pregnancy. (Apparently glamorising sex is all right, especially if it serves some transcendent purpose such as selling shampoo, but glamorising motherhood crosses the line.)

Having a baby is not sad. The reason not to have a baby in your teens is the risk that it will spoil something in your future – maybe your family life, your career or your economic prospects. In their landmark study of unmarried mothers, Promises I Can Keep, the US sociologists, Kathryn Edin and Maria Kefalas, noted that poor women need a “reason to wait” if they are to delay having children. It had better be a good reason. Time flies, after all. Whether or not a teenager’s having a child is a misfortune, teenagers themselves may see it as a lesser misfortune than a 40-year-old’s wishing for a child she cannot have.

The present ideology of family planning arose in a more fluid society than our own. It was constructed by college-educated baby-boom elites who, as they climbed from the middle into the upper-middle class, came to find pitiful the lives their mothers led as housewives. They chose careers over – or on top of – child-rearing and reaped substantial rewards. Whether those rewards are worth the risks of never having a child might be judged differently by the next generation.

As it gets harder to climb out of the class one was born in, the opportunity cost of being a young mother falls. Outside of the well-off, Ms Edin and Ms Kefalas note, the opportunity cost is already lower than it looks. Poor teen mothers “have about the same long-term earnings trajectories as similarly disadvantaged youth who wait until their mid or late twenties to have a child”. Given the increasing likelihood that a woman will raise her children alone, might not the teen years be a prudent time to become a single mother, while the financial and day-care resources of one’s own parents are still available?

Baby-boom feminists did not replace a superstitious attitude towards teen sexuality with a rational one. They replaced one set of priorities with another. Their careerism prevented teen motherhood as reliably as did their mothers’ moralism. The Gloucester girls appear equally unimpressed with both logics. If the old “pregnancy pact” that went by the name of marriage is no longer so readily available, they are not fools to look for a substitute.

The writer is a senior editor at The Weekly Standard

More columns at www.ft.com/caldwell