Image caption Children playing near derelict houses in Baltimore

It's not the $1m question. It's the million Swiss francs question.

It has become a depressingly universal truth in education that children from poorer backgrounds tend on average to do less well than their richer counterparts.

But what would happen if you took those poorer families and gave them money, real hard cash? If you make a poor family richer, will their children's chances of success rise accordingly?

Or is it much more complex?

Are children being held back not by lack of money, but by poverty's fellow travellers, such as bad housing, ill health, unemployment, chaotic parenting or family breakdown? Or are poor children getting stuck in a downward spiral of poorly educated parents and bad schools?

A US economist, Prof Greg Duncan, has won a million Swiss franc (£680,000) research prize to find out, in an annual award by the Zurich-based Jacobs Foundation, a charity that supports research into improving childhood.

Prof Duncan, an expert on the impact of poverty in childhood, wants to take a randomised group of a thousand low-income single mothers with a newborn child and give them $4,000 (£2,890) each for the first three years of the children's lives.

Another control group of mothers will get a much smaller amount.

Prof Duncan, from the School of Education at the University of California, Irvine, is going to to measure what happens next.

Brain development

The experiment will be a big, expensive, long-term venture, with the prize money supporting the pilot stage. But Prof Duncan wants this to answer some big questions about what happens if you reduce hardship in the earliest years.

Image caption Prof Greg Duncan wants to measure how raising income changes life chances

Can raising income deliver a measurable change in family life and children's progress? Will neuroscientists find a difference in cognitive development between those who receive the $4,000 and those who don't?

"We want to see whether we can find a direct link between poverty reduction and brain development in very young children," Prof Duncan says.

The idea of giving financial support to low-income families is well established - it underpins a range of family benefits, allowances and tax credits in many countries.

But what this study wants to discover is the specific impact of changing income in the years before school. Prof Duncan's earlier research has suggested strong links between experiences in the early years and how adults fare in later life.

This is the time when children are developing most rapidly, when the "architecture of the brain" is being established, he says.

There won't be any constraints on how these low-income families spend the extra money.

If families throw away the cash recklessly, rather than spending it on supporting children, that will be part of the findings.

Real-life spending

The purity of the experiment is to see what happens in the real world if poor young parents are made slightly less poor. Will their children's school performance be less poor as well?

Prof Duncan's research has highlighted how the achievement gap is already entrenched by the age of five, suggesting that intervention needs to come earlier.

Image caption If the odds begin to stack up against poor families, will cash be enough to reverse disadvantage?

Before pupils turn up for their first day at school, middle-class children are already ahead of their poorer classmates at such tasks as recognising letters or putting numbers in order.

And children who are poor at the age of five are on a downward track that makes them more likely to leave education earlier, earn less money and suffer poor health than richer children.

There are also striking differences in family structure. A poor girl is more than five times more likely to grow up and have children outside of marriage than her wealthier classmates.

The experiment, which is planned to launch in 2015, will try to establish to what extent living on a low income is the "active ingredient" in such different outcomes.

If parents are under less financial pressure, will they behave differently to their children? Will family time change with more spending power?

The study will try to separate the low-income effect from other factors such as family relationships, individual character and personal resilience.

The determination of individuals to succeed might be more relevant than a bank balance.

Climbing the ladder

This experiment has a particular resonance for the US education system.

In the past, even though the poor in the US might have lacked some social security "safety nets", Prof Duncan says there was a very valuable compensation from public investment in the education system. It provided a ladder upwards.

But that is no longer the case, he says.

Image caption A church charity providing food aid to families this month in Chicago

The US education system had been a world leader, a superpower in education as well as in economic and military terms.

But more recently it has faced a stream of bad news.

Last month, there was a new low ebb when the influential the Organisation for Economic Co-operation and Development think tank published research showing that young people in the US workforce had the lowest levels of maths skills in the developed world.

Such weaknesses in education have a great significance for the life chances of children born into poverty.

A major study this month from the independent Pew Research group, based in Philadelphia, looked at the factors that helped people born into low-income families in the US to rise up the income ladder.

Such "rags to riches" stories are more common in Hollywood movies than in real life, the study concludes.

But where people do beat the odds and rise up the ladder, the key factor is education. Getting a college degree is the surest route to social mobility, the research shows.

College graduates were over five times more likely to escape the bottom rung of the ladder.

Family structure was also a big influence. Two-parent families were more than three times as likely to move out of the lowest-income bracket compared with single-parent families.

The study shows that education and family are the dominant influences on escaping poverty.

What Prof Duncan's research will investigate is whether inserting cash into the equation can improve the odds of success.