Black boys raised in America, even in the wealthiest families and living in some of the most well-to-do neighborhoods, still earn less in adulthood than white boys with similar backgrounds, according to a sweeping new study that traced the lives of millions of children.

White boys who grow up rich are likely to remain that way. Black boys raised at the top, however, are more likely to become poor than to stay wealthy in their own adult households.

Even when children grow up next to each other with parents who earn similar incomes, black boys fare worse than white boys in 99 percent of America. And the gaps only worsen in the kind of neighborhoods that promise low poverty and good schools.

According to the study, led by researchers at Stanford, Harvard and the Census Bureau, income inequality between blacks and whites is driven entirely by what is happening among these boys and the men they become. Though black girls and women face deep inequality on many measures, black and white girls from families with comparable earnings attain similar individual incomes as adults.

“You would have thought at some point you escape the poverty trap,” said Nathaniel Hendren, a Harvard economist and an author of the study.

Black boys — even rich black boys — can seemingly never assume that.

The study, based on anonymous earnings and demographic data for virtually all Americans now in their late 30s, debunks a number of other widely held hypotheses about income inequality. Gaps persisted even when black and white boys grew up in families with the same income, similar family structures, similar education levels and even similar levels of accumulated wealth.