Image: Man with empty pockets © Digital Vision, Digital Vision Ltd.

The American Dream is as much about your kid's future as it is about buying that dream house or retiring comfortably. The script generally goes something like this: You work hard all your life, put your kids through college and watch as they live a better life than you did.

Unfortunately, it doesn't always play out that way.

According to a report by Pew's Economic Mobility Project, 28% of people who grew up in the middle class eventually fell down the income ladder. The report was assembled by analyzing the National Longitudinal Survey of Youth study, which looked at teenagers in 1979 and returned to assess their economic status between 2004 and 2006.

In many cases, the root cause of Americans' "downward mobility" is obvious. Failing to graduate from high school, for instance, greatly increased the chance that someone would fall out of the middle class.

But whether it happens to your child also has a lot to do with race, gender and drug use.

While just 21% of white men in the study fell out of the middle class (defined as those making from the 30th to the 70th percentile of U.S. income distribution), a whopping 38% of black men who grew up in the middle class wound up slipping down the ladder. The report found that much of this gap can be explained by existing differences between the two groups, including standardized test scores and environmental factors such as the occupational status of their fathers.

Less explainable are the differences between genders. While women of all races were equally likely to lose their middle-class status, white women were much more likely than white men to fall out of the middle class -- 30% of white women move down the economic ladder, versus just 21% of white men, a gap the report concludes is "almost completely unexplained."

Divorced? That financially devastating event makes it more likely for men and women alike to fall out of the middle class. But once again, women tended to come out worse: Divorced women were 38 percentage points more likely than average to find themselves falling below the middle-class threshold. And never getting married also increased the odds of downward mobility, especially among women.

Ultimately the report raises more questions than it answers. While it identifies differing test scores as the main culprit behind the racial divide in downward mobility, it nevertheless acknowledges that it can't explain why white men tend to perform much better on standardized tests. And it likewise calls for further research on the question of gender disparities and their impact on downward mobility.

Whatever the root causes, though, it's clear we're not all equally positioned to achieve the American Dream.