Most innovations in the field of child safety are affiliated with—shock of shocks—a new product to be marketed. (Nearly five million car seats are sold each year.) These products are often a response to some growing scare in which, as Peter Sandman might put it, the outrage outweighs the hazard. Compare the four hundred lives that a few swimming pool precautions might save to the number of lives saved by far noisier crusades: child-resistant packaging (an estimated fifty lives a year), flame-retardant pajamas (ten lives), keeping children away from airbags in cars (fewer than five young children a year have been killed by airbags since their introduction), and safety draw-strings on children’s clothing (two lives).

Hold on a minute, you say. What does it matter if parents are manipulated by experts and marketers? Shouldn’t we applaud any effort, regardless of how minor or manipulative, that makes even one child safer? Don’t parents already have enough to worry about? After all, parents are responsible for one of the most awesomely important feats we know: the very shaping of a child’s character. Aren’t they?

The most radical shift of late in the conventional wisdom on parenting has been provoked by one simple question: how much do parents really matter?

Clearly, bad parenting matters a great deal. As the link between abortion and crime makes clear, unwanted children—who are disproportionately subject to neglect and abuse—have worse outcomes than children who were eagerly welcomed by their parents. But how much can those eager parents actually accomplish for their children’s sake?

This question represents a crescendo of decades’ worth of research. A long line of studies, including research into twins who were separated at birth, had already concluded that genes alone are responsible for perhaps 50 percent of a child’s personality and abilities.

So if nature accounts for half of a child’s destiny, what accounts for the other half? Surely it must be the nurturing—the Baby Mozart tapes, the church sermons, the museum trips, the French lessons, the bargaining and hugging and quarreling and punishing that, in toto, constitute the act of parenting. But how then to explain another famous study, the Colorado Adoption Project, which followed the lives of 245 babies put up for adoption and found virtually no correlation between the child’s personality traits and those of his adopted parents? Or the other studies showing that a child’s character wasn’t much affected whether or not he was sent to day care, whether he had one parent or two, whether his mother worked or didn’t, whether he had two mommies or two daddies or one of each?

These nature-nurture discrepancies were addressed in a 1998 book by a little-known textbook author named Judith Rich Harris. The Nurture Assumption was in effect an attack on obsessive parenting, a book so provocative that it required two subtitles: Why Children Turn Out the Way They Do and Parents Matter Less than You Think and Peers Matter More. Harris argued, albeit gently, that parents are wrong to think they contribute so mightily to their child’s personality. This belief, she wrote, was a “cultural myth.” Harris argued that the top-down influence of parents is overwhelmed by the grassroots effect of peer pressure, the blunt force applied each day by friends and school-mates.

The unlikeliness of Harris’s bombshell—she was a grandmother, no less, without PhD or academic affiliation—prompted both wonder and chagrin. “The public may be forgiven for saying, ‘Here we go again,’” wrote one reviewer. “One year we’re told bonding is the key, the next that it’s birth order. Wait, what really matters is stimulation. The first five years of life are the most important; no, the first three years; no, it’s all over by the first year. Forget that: It’s all genetics!”

But Harris’s theory was duly endorsed by a slate of heavyweights. Among them was Steven Pinker, the cognitive psychologist and bestselling author, who in his own book Blank Slate called Harris’s views “mind-boggling” (in a good way). “Patients in traditional forms of psychotherapy while away their fifty minutes reliving childhood conflicts and learning to blame their unhappiness on how their parents treated them,” Pinker wrote. “Many biographies scavenge through the subject’s childhood for the roots of the grown-up’s tragedies and triumphs. ‘Parenting experts’ make women feel like ogres if they slip out of the house to work or skip a reading of Goodnight Moon. All these deeply held beliefs will have to be rethought.”

Or will they? Parents must matter, you tell yourself. Besides, even if peers exert so much influence on a child, isn’t it the parents who essentially choose a child’s peers? Isn’t that why parents agonize over the right neighborhood, the right school, the right circle of friends?

Still, the question of how much parents matter is a good one. It is also terribly complicated. In determining a parent’s influence, which dimension of the child are we measuring: his personality? his school grades? his moral behavior? his creative abilities? his salary as an adult? And what weight should we assign each of the many inputs that affect a child’s outcome: genes, family environment, socioeconomic level, schooling, discrimination, luck, illness, and so on?

For the sake of argument, let’s consider the story of two boys, one white and one black.

The white boy is raised in a Chicago suburb by parents who read widely and involve themselves in school reform. His father, who has a decent manufacturing job, often takes the boy on nature hikes. His mother is a housewife who will eventually go back to college and earn a bachelor’s degree in education. The boy is happy and performs very well in school. His teachers think he may be a bona fide math genius. His parents encourage him and are terribly proud when he skips a grade. He has an adoring younger brother who is also very bright. The family even holds literary salons in their home.

The black boy is born in Daytona Beach, Florida, and his mother abandons him at the age of two. His father has a good job in sales but is a heavy drinker. He often beats the little boy with the metal end of a garden hose. One night when the boy is eleven, he is decorating a tabletop Christmas tree—the first one he has ever had—when his father starts beating up a lady friend in the kitchen. He hits her so hard that some teeth fly out of her mouth and land at the base of the boy’s Christmas tree, but the boy knows better than to speak up. At school he makes no effort whatsoever. Before long he is selling drugs, mugging suburbanites, carrying a gun. He makes sure to be asleep by the time his father come home from drinking, and to be out of the house before his father awakes. The father eventually goes to jail for sexual assault. By the age of twelve, the boy is essentially fending for himself.

You don’t have to believe in obsessive parenting to think that the second boy doesn’t stand a chance and that the first boy has it made. What are the odds that the second boy, with the added handicap of racial discrimination, will turn out to lead a productive life? What are the odds that the first boy, so deftly primed for success, will somehow fail? And how much of his fate should each boy attribute to his parents?

One could theorize forever about what makes the perfect parent. For two reasons, the authors of this book will not do so. The first is that neither of us professes to be a parenting expert (although between us we do have six children under the age of five). The second is that we are less persuaded by parenting theory than by what the data have to say.

Certain facets of a child’s outcome—personality, for instance, or creativity—are not easily measured by data. But school performance is. And since most parents would agree that education lies at the core of a child’s formation, it would make sense to begin by examining a telling set of school data.