Now, with the publication of his new book, (Cornerstone), Tough is already causing controversy. A "provocative" new child-rearing book is "devastating New York's pushiest parents", is one of the milder comments so far.

Qualities such as perseverance, curiosity, conscientiousness, optimism and self-control, he writes, are more likely to ensure a child's success in life than "cognitive" (the traditional process of acquiring knowledge) teachings. The middle classes in both the US and Britain may feel sympathetic, guilty and angry about the educational and developmental issues facing disadvantaged children globally, but there's an unspoken relief that their children have been spared those particular obstacles.

They won't like to be told that they're also failing to prepare their children for adulthood. And they won't like to be told that exposing their children to stress or cosseting and placing an excessive emphasis on academic testing may condemn their progeny to similarly bleak outcomes.

"I certainly think it's easier to be rich than poor," says Tough. "The kids I've met growing up in poverty have obstacles that the rest of us don't. But there is a growing literature about the particular psychological problems advantaged kids grow up having."

One study in the book concludes that "licked and groomed" rat pups are better able to combat the stresses of life than children of affluent parents who cannot connect to them. But "helicopter parenting" - hovering over your kids, overprotective and hyper-attentive - can be just as harmful where character development is concerned. Tough is the father of a three-year-old boy, Ellington, and he describes how hard it is to stop himself from trying to protect his boy from every bump and tumble, certain in "the knowledge that if we want him to succeed, we need to let him fail. Or more precisely, we need to let him manage failure."

Tough stresses the importance of failure as a key character-building tool. If we do not let our children fail - from the bumps and knocks of the first few years to losing childhood games and sports - they will not develop strong enough "characters" to survive later on in life. "Character" is a term we often wrongly use to describe something innate and unmalleable - something that defines us from birth. And while neuroscientists may tell us that a person's character is roughly half genetic and half nurture, Tough believes that environment matters more than we think.

"We tend towards biological explanations because it makes things easier, but early experiences matter a great deal. When psychologists looked at the temperament of a six-month-old and then examined that same child aged 30, they found correlations. That means that what happened in the first six months is crucial."

There are two particularly fruitful periods early on in a child's life, the first being well before they enter the school system, "in the first 18 months", says Tough. "That's when psychologists talk about the importance of 'attachment'."

Does he mean love? "That's a part of it, certainly, but specifically they talk about 'attunement': how much you are attuned to what your toddler is trying to say to you. When a child is trying to express what they want and they feel that someone is responding to them, that's really beneficial to their development."

The second period is adolescence, when children are able to reflect on their own character strengths - and possibly change them. "These huge transformations can happen with kids around that time, and the decisions you make during that period - getting pregnant, doing drugs, turning to crime or dropping out - can affect your whole life."

The difficulties some children are facing later on in life can only partly be blamed on their parents' failure to instil "good character" - which Tough defines as curiosity, perseverance and generosity of spirit - in those early years when the prefrontal cortex (the part of the brain where character develops) is at its most plastic.

Among the many specialists Tough references in his book is Suniya Luthar, a researcher and professor of psychology at Columbia University, who composed a study of children growing up in affluence. Luthar says the pressure children are under to succeed - "and that means trophies and test scores and getting into the right college" - can also be counterproductive. Traditional methods of assimilating knowledge, by rote learning, for example, do not necessarily prepare children for a successful future.

"Of course parents can do an awful lot to affect their child's psychological and emotional character, but schools can also," Tough insists. "And when kids grow up without the right kind of support and environment at home, schools can do a lot to compensate for that."

"Character schooling", however, remains an elusive science. "You have to first think about what kind of character you're talking about. There are performance character strengths and moral character strengths, and when you look at existing character education programmes in the US, a lot of them focus on the moral: honesty, integrity sharing, inclusiveness."

What became known as "the self-esteem" movement, when a group of psychologists in the 90s decided that the idea of "winners" and "losers" in schools was damaging children - the "all must have prizes" mentality - has been proved wrong time and time again, says Tough.

Tough is the first to concede that many of the conclusions in may sound "warm and fuzzy", but, he insists, they're based in cold, hard science. He admits he dropped out of college (twice) - but says he might not have done if he had had the kind of character skills he prizes instilled in him as a young man. Yet few would question Tough's success in life.

And while so many books on education are essentially pessimistic in tone, the optimism he sees as being so crucial to our children's development is clearly there, in his writing. "I am hopeful," he smiles. "There's a lot of bad news out there about how rich kids and poor kids are doing educationally. If the right interventions happen, change is possible. It might just take a while. It might take forever."