Nearly one in three Americans who grew up in the middle class has slipped down the income ladder as an adult, according to a new report by the Pew Charitable Trusts.

Downward mobility is most common among middle-class people who are divorced or separated from their spouses, did not attend college, scored poorly on standardized tests, or used hard drugs, according to the report.

“A middle-class upbringing does not guarantee the same status over the course of a lifetime,” the report says.

The study focused on people who were middle-class teenagers in 1979 and who were between 39 and 44 years old in 2004 and 2006.

It defines people as middle-class if they fall between the 30th and 70th percentiles in income distribution, which for a family of four is between $32,900 and $64,000 a year in 2010 dollars.

People were deemed downwardly mobile if they fell below the 30th percentile in income, if their income rank was 20 or more percentiles below their parents’ or if, in absolute terms, they earn at least 20 percent less than their parents.

The findings do not cover the difficult times that the nation has endured since 2007.

The report found that being married helps people avoid the worst economic outcomes. Women who are divorced, widowed or separated are much more likely to fall down the economic ladder than their married counterparts.

For men, the differences are not as dramatic, although married men are more likely than single men to retain their middle-class status as adults.

Education, particularly going to college, is another crucial factor in people’s economic stability, the report says.

Women who graduated from high school are more likely to be downwardly mobile than their counterparts who are college graduates. The same dynamic exists among men, the study found.

Over all, African American men have a particularly hard time clinging to middle-class status. Thirty-eight percent of black men who grew up middle-class are downwardly mobile, nearly double the rate of white men, the report says.

Hispanic men are slightly more likely than white males to fall down the economic ladder, but the difference was not statistically significant.

Among African Americans and Hispanics, men are more likely to slip than women, although the reverse is true among whites.

The racial gap in mobility has perplexed researchers at Pew since a 2007 report that said nearly half of African Americans born to middle-income parents in the late 1960s plunged into poverty or near-poverty as adults.