Developmental psychologists have found themselves on the defensive since Judith Rich Harris published her 1998 book, "The Nurture Assumption" (Free Press). In it, Harris asserts that parents have little or no influence over the long-term development of their children's personality.

Putting together evidence from several areas of psychology and sociology, Harris concluded that personality is shaped by the experiences children have outside the home--in particular, experiences with peers--and that any similarities between parents and children are due to shared genes and a shared culture. Her ideas garnered widespread media attention, including an oft-cited article in The New Yorker.

In response, the National Institute of Child Health and Human Development (NICHD) and the Robert Wood Johnson Foundation sponsored a conference on parenting last summer. The fruit of this conference is a book, "Parenting and the Child's World: Influences on Academic, Intellectual and Socioemotional Development," to be published next year by Erlbaum. Chapters by Harris and behavioral geneticist David Rowe, PhD, present data to support Harris's view, while a cadre of developmental psychologists detail decades of research that they feel demonstrates the role parents play in influencing children's development.

Their foremost conclusion?

"Parenting matters," says developmental psychologist John Borkowski, PhD, co-editor of the book with Sharon Ramey, PhD.

That's not to say that genes and peers don't, but the book makes no attempt to weigh the three in terms of which factor is more or less important.

"The idea was to figure out when, where and how parenting matters," says Borkowski, professor of psychology at the University of Notre Dame.

Along with parenting style and disciplinary approaches, parents influence the schools their children attend, the foods they eat and even the neighborhood--by choice or circumstances--in which they grow up.

"Parenting influences are much more than parents' desires to mold children," says Ramey, director of the Civitan International Research Center at the University of Alabama at Birmingham. "Can you make your child be who you want? Of course not."

But to even engage the question, "Do parents matter?"--as many journalists have since Harris published her book--is preposterous, say Ramey and other contributors to the book.

But it's equally inappropriate, as some developmental researchers have done, to even try to talk about direct effects of parenting, genes or social environment because all three are acting in conjunction with each other and influencing each other, say University of California, Berkeley, husband-and-wife research team Carolyn Cowan, PhD, and Philip Cowan, PhD, who wrote a chapter for the book.

"It's like talking about a horse race and trying to pit two horses against each other when there are 10 in the race," says Philip Cowan. "You can't isolate the two from the pack because they're inseparably linked to the other horses on the track."

Bi-directional influences

Many of the chapters in the book agree that, in the early days of child development research, the emphasis was too heavily weighted toward parental influences. Today, however, most researchers have become more sophisticated in their theories and studies and examine parenting as one of many factors influencing child development.

"We now see parenting less in terms of simple parent-to-child influence, and more as a set of interactive processes whereby parents and children react to each other and influence each other from the moment a child is born," writes Stanford University's Eleanor Maccoby, PhD, in one of the book's introductory chapters.

This model of bi-directional influences can be used to explain some of the same findings from behavioral genetics research that Harris uses to argue that parenting style has little influence on certain behavioral traits, such as personality, says Maccoby.

The behavioral genetics work finds that genes account for as much as 50 percent of the variance in certain behavioral traits and that siblings' shared environment--the home and parenting--has little influence on these traits.

But, argues Maccoby, other studies show that a given parenting style can have different effects on children with different temperaments. The result is that parenting can function to make children in the same family different rather than alike.

"In other words," she writes, "the home environment that children share is indeed having an effect, even though it is a different effect for different children and would not be computed as a shared effect in a behavior genetics analysis."

Implications from interventions

A main problem with linking parenting definitively to child development is that most of the research is necessarily correlational, say the Cowans.

That's in part why the Berkeley developmental researchers turned to intervention studies to examine the role of parenting in children's academic success. Their studies have been designed like randomized clinical trials--randomly assigning families to an intervention or control group. The intervention families participate in a type of couples group intervention in which mothers and fathers work on parenting issues as well as issues related to their relationships as couples.

In a study that targeted parents whose children were about to enter school, they found that improving either parenting practices or the marital relationship had a significant effect one, two and then four years later on children's behavior and success in school. The marital intervention had a bigger effect on lowering children's aggression and academic performance while the parenting intervention had a greater influence on reducing shy and withdrawn behavior.

Interestingly, a byproduct of the marital intervention was that, in addition to showing less conflict as a couple, parenting styles improved too--these parents were warmer and provided more structured discipline to their children. The parenting intervention, in contrast, did not influence parents' relationships. Overall, the more parents changed after the couples group intervention, the better their children did in school, says Carolyn Cowan.

Although the Cowans believe intervention studies are the best way to confirm a link between parenting and child development, they don't underestimate the power of correlational and longitudinal research. Without correlational research on parenting, there would be nothing on which to base an intervention, they say.

For example, over the past several decades University of Minnesota psychologist Alan Sroufe, PhD, and his colleagues have followed children from infancy into adulthood, documenting the link between early parent­child attachment and outcomes, such as school success and failure, social competence and psychopathology. Such studies provide compelling evidence on their own, as well as a foundation for conducting intervention studies designed to promote secure attachment in at-risk children.

"At the end of this century, there is abundant evidence for the critical role of the caregiving experience for the development of the child, including prospective longitudinal data," writes Sroufe in his chapter. "While the evidence two decades ago may have been ambiguous, this is no longer the case."

With that said, researchers may never be able to put a number on how big an influence parents have on their children, says Loyola University's Fred Morrison, PhD, who studies the influence of parenting on school achievement. In terms of academics, some recent studies suggest that 50 percent of the variation between high-and low-functioning children results from influences that occur before children enter school. But even the half that results from influences after children start school may be mediated by family factors. For example, Morrison and his colleagues find that social skills, including a child's ability to sit still and concentrate, have an effect on academic performance.

"All of these things are intertwined," says Morrison. "And parenting adds up to a lifestyle that funnels into the language, general knowledge, reading and math skills that children start school with."

Meanwhile, none of the arguments or studies by developmental psychologists dissuades Harris from her view that genes and outside-the-home environment have a greater influence than parents on children's personality development, she says. Indeed, in her chapter in the forthcoming book, she criticizes the methodology of intervention studies and points out that Maccoby's explanation of sibling differences--that children born with different temperaments will react in different ways--cannot account for the personality differences between identical twins reared in the same home.

Nonetheless, Borkowski and Ramey tie the book together with a final chapter that uses the research presented in the book to provide parents with useful information about best parenting practices and policy-makers with broadly based guidelines for more effective intervention programs.

As a spin-off from the book, Borkowski and Ramey are working with NICHD to translate the parenting recommendations into a parent-geared pamphlet that will be available early next year.