WASHINGTON -- We're not who we think we are.

The American self-image is suffused with the golden glow of opportunity. We think of the United States as a land of unlimited possibility, not so much a classless society but as a place where class is mutable -- a place where brains, energy and ambition are what counts, not the circumstances of one's birth. But three important recent studies suggest that Horatio Alger doesn't live here anymore.

The Economic Mobility Project, a research initiative led by the Pew Charitable Trusts, looked at the economic fortunes of a large group of families over time, comparing the income of parents in the late 1960s with the income of their children in the late 1990s and early 2000s. Here's the finding that jumps out at me:

"The 'rags to riches' story is much more common in Hollywood than on Main Street. Only 6 percent of children born to parents with family income at the very bottom move to the very top."

That's right, just 6 percent of children born to parents who ranked in the bottom fifth of the study sample, in terms of income, were able to bootstrap their way into the top fifth. Meanwhile, an incredible 42 percent of children born into that lowest quintile are still stuck at the bottom, having been unable to climb a single rung of the income ladder.

The Economic Mobility Project can't be accused of having any kind of ideological bias; it's a collaboration, led by Pew, involving four leading think tanks that pretty much cover the political spectrum -- the American Enterprise Institute, the Brookings Institution, the Heritage Foundation and the Urban Institute.

"Both left and right can care about this," said John Morton, Pew's managing director for economic policy. "Traditionally, Americans have been ready to accept high levels of inequality because of our belief in the American dream. What happens if we can't believe in the dream any longer?"

When the three studies were released this fall, most reporters focused on the finding that African-Americans born to middle-class or upper middle-class families are earning slightly less, in inflation-adjusted dollars, than did their parents. Julia Isaacs, the Brookings scholar who wrote the reports, said the reason for this anomaly is unclear; overall, the data suggest that black people are somewhat less upwardly mobile than white people, although about two-thirds of African-Americans earn more than their parents did.

Isaacs said she was surprised at finding that the personal income of U.S. men has been almost perfectly flat for the past three decades. One of Isaacs' studies indicates, in fact, that most of the financial gains white families have made in that time can be attributed to the entry of white women into the labor force. This is much less true for African-Americans; in 1968, when the sample group was first surveyed, black women were far more likely to already have income-producing jobs.

The picture that emerges from all the quintiles, correlations and percentages is of a nation in which, overall, "the current generation of adults is better off than the previous one," as one of the studies notes. The median income of the families in the sample group was $55,600 in the late 1960s; their children's median family income was measured at $71,900. However, this rising tide has not lifted all boats equally.

Even more troubling is that our notion of America as the land of opportunity gets little support from the data. Americans move fairly easily up and down the middle rungs of the ladder, but there is "stickiness at the ends" -- four out of 10 children who are born poor will remain poor, and four out of 10 children who are born rich will stay rich.

The Economic Mobility Project's work should be part of the political debate. Every candidate for president should read these studies and then explain why it's acceptable that a poor kid has only a 6 percent chance of reaching the top.