SHANA, a bright and chirpy 12-year-old, goes to ballet classes four nights a week, plus Hebrew school on Wednesday night and Sunday morning. Her mother Susan, a high-flying civil servant, played her Baby Einstein videos as an infant, read to her constantly, sent her to excellent schools and was scrupulous about handwashing.

Susan is, in short, a very conscientious mother. But she worries that she is not. She says she thinks about parenting “all the time”. But, asked how many hours she spends with Shana, she says: “Probably not enough”. Then she looks tearful, and describes the guilt she feels whenever she is not nurturing her daughter.

Susan lives in Bethesda, an azalea-garlanded suburb of Washington, DC packed with lawyers, diplomats and other brainy types. The median household income, at $142,000, is nearly three times the American average. Some 84% of residents over the age of 25 are college graduates, compared with a national norm of 32%. Couples who both have advanced degrees are like well-tended lawns—ubiquitous.

Bethesda moms and dads take parenting seriously. Angie Zeidenberg, the director of a local nursery, estimates that 95% of the parents she deals with read parenting books. Nearly all visit parenting websites or attend parenting classes, she says.

Bethesda children are constantly stimulated. Natalia, a local four-year-old, watches her three older siblings study and wants to join in. “She pretends to have homework,” says her mother, Veronica; she sits next to them and practises her letters.

Veronica is an accountant; her husband is an engineer. Their children “all know that school doesn’t end at 18,” says Veronica. “They assume they’ll go to college and do a master’s.” Asked how often she checks her various children’s progress on Edline, the local schools’ website that shows grades in real time, she admits: “More than I should, probably.”

In “Coming Apart”, Charles Murray, a social scientist, ranked American zip codes by income and educational attainment. Bethesda is in the top 1%. Kids raised in such “superzips” tend to learn a lot while young and earn a lot as adults. Those raised in not-so-super zips are not so lucky.

Consider the children of Cabin Creek, West Virginia. The scenery they see from their front porches is more spectacular than anything Bethesda has to offer: the Appalachian Mountains rather than the tree-lined back streets of suburbia. But the local economy is in poor shape, as the coal industry declines. The median household income is $26,000, half the national average. Only 6% of adults have college degrees. On Mr Murray’s scale, Cabin Creek is in the bottom 10%.

Melissa, a local parent, says that her son often comes home from school and announces that he has no homework. She does not believe him, but she cannot stop him from heading straight out across the creek to play with his friends in the woods.

She has other things to worry about. The father of her first three children died. The father of her baby is not around. Her baby suffers from a rare nutritional disorder. And Melissa has to get by on $420 a month in government benefits. Small wonder that she struggles to enforce homework. And small wonder the gap between haves and have-nots in America is so hard to close.

Parenting has changed dramatically in the past half-century. When labour-saving products such as washing machines, dishwashers and ready meals started to spread, people naturally assumed that parents would soon have much more free time.

Not so. Although the average American couple spent eight hours a week less on household chores in 2011 compared with 1965, according to the Pew Research Centre, more than all of this extra time was gobbled up by child care (see chart 1). Women now devote an extra four hours a week to looking after their offspring; men devote an extra four and a half. This is largely a good thing. For most people, teaching a kid to ride a bike is more rewarding than washing dishes. A different Pew survey finds that 62% of parents find child care “very meaningful”, a figure that falls to 43% for housework and only 36% for paid work.

However, there are two worries about modern parenting. One concerns “helicopter parents” (largely at the top of the social scale), who hover over their children’s lives, worrying themselves sick, depriving their offspring of independence and doing far more for them than is actually beneficial. This gets a lot of attention, probably because media folk belong to the helicoptering classes (see article). The other worry concerns parents at the bottom, who struggle to prepare their children for a world in which the unskilled are marginalised. This is far more important. In a study in 1995, Betty Hart and Todd Risley of the University of Kansas found that children in professional families heard on average 2,100 words an hour. Working-class kids heard 1,200; those whose families lived on welfare heard only 600. By the age of three, a doctor’s or lawyer’s child has probably heard 30m more words than a poor child has. Well-off parents talk to their school-age children for three more hours each week than low-income parents, according to Meredith Phillips of the University of California, Los Angeles. They put their toddlers and babies in stimulating places such as parks and churches for four-and-a-half more hours. And highly educated mothers are better at giving their children the right kind of stimulation for their age, according to Ariel Kalil of the University of Chicago. To simplify, they play with their toddlers more and organise their teenagers.

The Adventures of Supermom

“I talk to him constantly,” says Lacey, another Bethesda mother, of her two-year-old son. “As we go through the day, I talk about what we’re doing. I try to make the regular tasks interesting and fun, like going to the grocery store.” Her older son, who is five, devours maths apps and asks his mother questions about arithmetic. At the weekend the family might go to the American History Museum or the Washington Zoo or a park.

Cabin Creek parents love their children just as much as Bethesda parents do, but they read to them less. It doesn’t help that they are much more likely to be raising their children alone, like Melissa. Only 9% of American women with college degrees who gave birth in the past year are unmarried; for those who failed to finish high school the figure is 61%. Two parents have more time between them than one.

And even two-parent families in Cabin Creek tend to be more stretched than those in Bethesda. Sarah, another Cabin Creek mom, has a sick mother and a husband who was injured in a coal mine. Her three boys, two of whom make it a point of pride to be on the naughty kids list at school, exhaust her. She helps them with their homework and reads to them fairly regularly, but often just lets them watch television. “Dora the Explorer” is somewhat educational, she says: “It’s got Spanish in it.”

Children with at least one parent with a graduate degree score roughly 400 points higher (out of 2,400) on the Scholastic Aptitude Test (a test used for college entrance) than children whose parents did not finish high school. This is a huge gap. It is hard to say how much it owes to nurture and how much to nature. Both usually push in the same direction. Brainy parents pass on their genes, including the ones that predispose their children to be intelligent. They also create an environment at home that helps that intelligence to blossom, and they buy houses near good schools.

Nonetheless, there is evidence that parenting matters. After reading enough scholarly papers to make a life-sized papier-mâché elephant, Richard Reeves of the Brookings Institution, a think-tank, concludes that it accounts for about a third of the gap in development between rich and poor children. He argues that the “parenting gap” is more important than any other.

The two aspects of parenting that seem to matter most are intellectual stimulation (eg, talking, reading, answering “why?” questions) and emotional support (eg, bonding with infants so that they grow up confident and secure). Mr Reeves and his Brookings colleague Kimberly Howard take a composite measure of these things called the HOME scale (Home Observation for Measurement of the Environment) and relate it to how well children do in later life, using data from a big federal survey of those born in the 1980s and 1990s.

The results are striking. Some 43% of mothers who dropped out of high school were ranked among the bottom 25% of parents, as were 44% of single mothers. The gap between high- and middle-income parents was small, but the gap between the middle and the bottom was large: 48% of parents in the lowest income quintile were also among the weakest parents, compared with 16% of the parents in the middle and 5% in the richest (see chart 2).

Likewise, the difference between high-school dropouts and the rest was far greater than the gap between high-school and college graduates. Mr Reeves and Ms Howard estimate that if moms in the bottom fifth were averagely effective parents, 9% more of their kids would graduate from high school, 6% fewer would become teen parents and 3% fewer would be convicted of a crime by the age of 19. From a public-policy perspective, nature is a given. Individuals can influence the genes their children inherit, by choosing the right partner, but the state is concerned only with how children are nurtured. America lavishes public money on school-age children (more than $12,000 per pupil each year, or nearly one and a half times the rich-country average) but virtually ignores the very young, despite strong evidence that the earliest years matter most. Only 67% of American three- to five-year-olds and 42% of under-threes are enrolled in formal child care or preschool. In France it is 100% and 48%. Government meddling in parenting is politically touchy. As Mr Reeves writes: “Conservatives are comfortable with the notion that parents and families matter, but too often simply blame the parents for whatever goes wrong. They resist the notion that government has a role in promoting good parenting.” As for liberals, they have “exactly the opposite problem. They have no qualms about deploying expensive public policies, but are wary of any suggestion that parents—especially poor and/or black parents—are in some way responsible for the constrained life chances of their children.” Nothing the government can do will give the children of Cabin Creek the same life chances as the children of Bethesda. But weak parents can learn to be stronger, and outsiders can sometimes help them. In West Virginia, for example, an organisation called Parents as Teachers sends “parent educators” to families. They find them via the local maternity clinic, visit their homes and identify the parents most in need of help by looking for simple clues. For example, are there fewer than ten books visible? Does the family go out less than once a week?

The parent educators don’t just nag parents to read to their offspring more and hit them less. They also teach them how to interact with their kids in ways that stretch their minds: reasoning with them, answering their questions and teaching them basic skills. “I see a lot of parents doing things for their children because it saves time,” says Heather Miller, a parent educator. “Even one mom who tied her 12-year-old son’s laces. You have to learn to stop and let him do things for himself.”

A home visit is supposed to be fun. Visiting a five-year old called Lily, Ms Miller brings a game called “Five Little Monkeys”, based on a popular nursery rhyme. It involves numbers, artful propaganda in favour of going to sleep and the thrill of watching plastic monkeys fall off a spring-loaded bed. Lily plays merrily, though her commentary is revealing. Asked to mime brushing her teeth, she says she uses bottled water because the stuff from the tap is “bad”. (A recent chemical spill polluted the nearby river.)

When Lily was 18 months old, she did not talk. Parents as Teachers had her checked out and found that it was nothing to do with her intelligence: she simply had weak muscles in her mouth. The cure was cheap and jolly: her mom was shown how to tear up little bits of paper, scatter them on a table and dare Lily to blow them off through a straw. This strengthened her mouth muscles; now she chatters non-stop.

Helping parents teach

Parent educators hand out books as presents for the kids and offer leaflets to the parents. “Of the nine families I see, none buy[s] parenting books. But most look at the material I leave,” says Jennifer Parsons, another parent educator. The programme in West Virginia is cheap: about $1,800 per family each year. It has not been around long enough for its effectiveness to be assessed, but others have. A review of 11 home-visiting programmes by the federal health department found that seven led to at least two lasting benefits (eg, making the child healthier or better-prepared for school). A pre-school programme called HIPPY, which aims to teach parents how to be their children’s first teachers, appears to boost reading scores significantly.

Do such benefits last? In the 1960s a group of vulnerable pre-schoolers in Michigan were randomly selected either to enroll in a programme of daily coaching from well-trained teachers plus weekly home visits, or to join a control group. The early results were amazing: after a year the kids who took part were outscoring the control group by ten IQ points.

Disappointingly, that difference faded by the age of ten, leading many to doubt that the Perry project (named after the school where it took place) actually worked. However, even if it didn’t boost their IQ scores for long, the intervention appears to have taught them other useful skills, such as self-discipline and perseverance. The Perry pre-schoolers were far more likely than the control group to graduate from high school on time (77% to 60%). And by the age of 40, they were more likely to earn $20,000 a year or more (60% to 40%) and less likely to have been arrested five times or more (36% to 55%).

Perry generated $16 of benefit for every $1 spent on it, by one estimate. Another pre-school programme in Chicago showed a benefit-to-cost ratio of 10 to 1; the Elmira project in upstate New York was five to one; the Abecedarian project in North Carolina was four to one.

All this suggests that, when it comes to education, the best returns will come not from pumping yet more money into schools but from investing in the earliest years of life. And that includes lending a helping hand to parents who struggle.

Correction: An earlier version of this article confused the names of two organisations and referred to "Parents as Teachers" as "Zero to Three".