A strain running through the unfolding Barack Obama chronicles is the classic ''America, the land of opportunity'' theme: Where in the world could an African student arrive poor as dirt, strive for an education, make a life and have his American-born child rise within reach of (and perhaps grab) the nomination to be president of the United States?

The answer is likely to come back: Only in America. It goes to the notion that America offers the opportunity, and what anyone does with it is up to him or her. Work hard, and you can be all that you want to be.

The understanding, then, is that the American Dream rests deeper than, for instance, acquiring a house of one's own. The Dream begins first with the opportunity to grow legs, as it were, to stand on and to climb up. The Obama story, like innumerable others, is told and retold to reinforce the American way: equal opportunity — not necessarily equal results — no matter how humble anyone's beginnings.

The thing is, if opportunity truly is the quintessential American value, then nothing should be more important than making sure no one is deprived of basic opportunities to grow the ''legs'' strong enough to carry him or her upward.

These days, the strength of those legs depends on education, and perhaps more important, on opportunities to acquire the right education as much it does on individual abilities.

Increasingly, researchers are warning that younger Americans can no longer assume they will surpass their parents' generation in upward mobility. Is America still the wide open, fabled land of opportunity?

The Pew Charitable Trusts and four of the nation's think tanks have been exploring the question of mobility and opportunity. The goal of the initiative, the Economic Mobility Project, is to present ''an accurate picture of the status and health of the American Dream.''

One of the latest releases in a series of reports tackles some of the key questions that provoke no end of arguments. We know that education matters, but how much education for a level playing field? We know family background and social situations affect a child's economic prospects, but how big an influence? And what is, or should be, the role of government in driving economic mobility?

In many ways, the report on education, ''Education and Economic Mobility,'' confirms much that is fast becoming conventional knowledge about the economic value of education.

Yes, the report affirms that education matters a good deal, especially in poor families with incomes in the bottom 20 percent. With each level of completed education after high school, incomes rise. The difference between a high school diploma and a college degree was $29,000 a year in 2005.

It doesn't hurt to get more education. In each income group, from the bottom 20 percent of the population to the top 20 percent, a higher percentage of adult children who earned a college degree exceeded their parents' income, even the wealthiest parents.

And yes, children from wealthy family have a clear advantage. As the report notes, ''one way wealthy parents pass along their advantages to their children is by ensuring that they attend and graduate from college.'' For the poor, hard work helps improve the odds of doing economically much better than their parents.

To many such findings, the temptation may be to respond: ''But we knew that already.'' Other conclusions should invite a decidedly less smug response. Spend a moment with this concluding observation from the report:

''At every level from preschool, to the K-12 system, to the nation's colleges and universities, education has only modest economic impacts on the average low-income child or adolescent. Although education can and sometimes does boost the achievement and later income of children from relatively poor families, the average effect of education at all levels is to reinforce the differences associated with the family background that children and adolescents bring with them to the classroom.''

Few institutions in America represent the value of opportunity or the role of equalizer more than the public education system. Over time, we have come to regard public education as the great leveler, with the potential to erase those inequities over which children have no influence. What this report tells us is that when it comes to that most basic of American values, equalizing educational opportunity, we are not doing nearly well enough.