3 December 2012 Last updated at 19:03 By Sean Coughlan BBC News education correspondent An integral part of the American Dream is under threat - as "downward mobility" haunts the education system in the United States. The idea of going to college - and the expectation that the next generation will be better educated and more prosperous than its predecessor - has been hardwired into the ambitions of the middle classes in the United States. But there are deep-seated worries about whether this upward mobility is going into reverse. Andreas Schleicher, special adviser on education at the Organisation for Economic Co-operation and Development (OECD), says the US is now the only major economy in the world where the younger generation is not going to be better educated than the older. "It's something of great significance because much of today's economic power of the United States rests on a very high degree of adult skills - and that is now at risk," says Mr Schleicher. "These skills are the engine of the US economy and the engine is stuttering," says Mr Schleicher, one of the world's most influential experts on international education comparisons. Lack of opportunity The annual OECD education statistics show that only about one in five young adults in the US reaches a higher level of education than their parents - among the lowest rates of upward mobility in the developed world. For a country whose self-image is based on optimism and opportunity, the US is now a country where someone with poorly-educated parents is less likely to reach university than in almost any other industrial country. It's the opposite of a Hollywood ending. And about one in five young adults in the US are now defined in educational terms as "downwardly mobile" - such as children who have graduate parents but who don't reach university level themselves. When the global story of higher education is so much about rapid expansion and the race to increase graduates, it's almost counter-intuitive to find a powerhouse such as the United States on the brink of going backwards. It's easy to overlook the dominance of US higher education in the post-war era - or how closely this was linked to its role as an economic, scientific and military superpower. The US had the first great mass participation university system. The GI Bill, which provided subsidies for a generation of World War II veterans, supported three times as many people as are currently in the entire UK university sector. An American born in the 1950s was about twice as likely to become a graduate as someone born in the rest of the industrialised world. As the cars ran off the production lines in Detroit, rising numbers of graduates were leaving universities to become part of an expanding middle class. Overtaken But the US university system is no longer the only skyscraper on the block. It's been overtaken by rivals in Asia and Europe. Today's young Americans have a below-average chance of becoming a graduate, compared with other industrialised economies. The US Education Secretary Arne Duncan, in a speech a few weeks ago, asked how the US had in "the space of a generation" tumbled from first place to 14th in graduation rates. So what's gone wrong? The spiralling cost of higher education in the United States is often cited as a barrier - and the collective student debt has exceeded a trillion dollars. But Andreas Schleicher argues that a deeper problem is rooted in the inequalities of the school system. He says that the level of social segregation and the excessive link between home background and success in school is "cutting off the supply" between secondary school and university. The meritocratic, migrant energy in US culture is no longer operating in the school system. "If you lose the confidence in the idea that effort and investment in education can change life chances, it's a really serious issue," says Mr Schleicher. Middle-class squeeze A US Senate committee examined this sense of imperilled optimism, in a hearing called Helping More Young People Achieve the American Dream. The economist Miles Corak was among the expert witnesses - and he says the US education system reflects a wider picture of the "hollowing out" of the middle class. What you're seeing is the inequality of the labour market being echoed in education. Prof Corak describes a polarising jobs market, with the very rich and very poor diverging - and a collapse in jobs in the middle ground, such as clerical or manufacturing jobs. For such families, sending their children to college had once been a "defining metaphor for the country." But it seems that the education system is no longer holding the door open to the brightest and the best, regardless of background. The Philadelphia-based Pew research group compared the outcomes of young people in 10 western countries, in a project called Does America Promote Mobility as Well as Other Countries? It found the US had the strongest link between family wealth and educational success - and the lowest mobility. Advantage and disadvantage were being further amplified in education. Research manager Diana Elliott says in the US "income has a pervasive hold on mobility." Insecurity Another study by Pew, against the backdrop of recession, examined the phenomenon of downward mobility and found that a third of adults classified as middle class would slip out of that status during their adult life. It reflected a modern sense of insecurity, where families could no longer assume their children would be as prosperous. In fact, about a quarter of children born into the middle class were expected to slip downwards. None of this matches the image of the US as a place for fresh starts and self-made millionaires. Modern American history almost assumes an upward incline. But evidence of this downward drift has been gathering in recent years. A study by the University of California, Berkeley, showed that school leavers in California in 1970 were more likely to stay on to higher education than their counterparts in 2000. In terms of international education, that's like finding out that athletes were running faster 40 years ago. Such current difficulties should not be mistaken for any kind of end-of-empire zeitgeist, says Philip Altbach, director of the Center for International Higher Education at Boston College. Instead he says it's a more practical question of money. The rising cost of higher education is a deterrent. And there is a wider question of finance for higher education at state level. He also says there is another "dirty little secret" of US higher education - that too many people who enrol at university fail to graduate - which pushes down the graduation rate in international comparisons. Bouncing back Andreas Schleicher also says there are reasons for optimism. Almost more than any other country, he says the US has the financial resources, the capacity and the flexibility to change course quickly and to catch up. There are already plans to recover lost ground. President Barack Obama has been re-elected with a promise that the US will regain its global first place in graduation rates by 2020. And as part of this drive, the American Association of Community Colleges, in a project called Reclaiming the American Dream, has an ambitious plan to create five million more college places. But it's an aspiration against a gloomy background. "The American dream has stalled," the association's report says, describing a society where typical family incomes having been falling for more than a decade. A child born poor in the United States today is more likely to remain poor than at any time in our history. Many other nations now outperform us in educational attainment and economic mobility, and the American middle class shrinks before our eyes. It's as if It's A Wonderful Life had been remade - without the happy ending.