The issue: Since the 1990s, there has been a growing recognition that where children grow up influences their success as adults. Most famously, the Moving to Opportunity demonstration, a Department of Housing and Urban Development program that began in 1994, showed that poor children who grow up in neighborhoods with low poverty rates fare better — in terms of health and even income and education aspects — than their counterparts in poorer neighborhoods. Policymakers and researchers since have been pushing for programs, like housing vouchers, that would help move children to places where they would have more opportunities.

Ellora Derenoncourt, a postdoctoral associate in the department of economics at Princeton, says that for black families, the Great Migration is a cautionary tale in how moving to opportunity could prove to offer no opportunity at all.

Historically, Northern cities offered much more upward mobility to both white and black children. That is one of the reasons that between 1910 and 1970, approximately six million black people migrated from the South to the North — fleeing racist Jim Crow laws and violence by groups like the Klan.

But at some point something changed. “That pattern [of upward mobility] persists for white families,” Derenoncourt says, “[but] it’s completely not true for black families anymore.” For black children, growing up in Northern cities like Philadelphia doesn’t offer any more opportunity in terms of upward mobility than growing up in the South.

What happened — and when? Derenoncourt studied the impact of black migration to Northern cities during the second wave of the Great Migration (1940-70) and analyzed the outcomes for black people today. She used a measure of upward mobility that she defines as “your adult income conditional on your parents’ economic status.” In other words, whether you are destined to rank economically as your parents did, or have the opportunity to climb up the ladder.

Using econometric tools, Derenoncourt compared cities that were a common Great Migration destination with the cities that received fewer black migrants from the South. She finds that these cities changed dramatically over the second half of the 20th century, from being “the best places to grow up as a black child in the U.S. historically, to now being among the worst places to do so.”

One tempting explanation: deindustrialization. Perhaps, cities like Philadelphia were appealing destination cities because of thriving industry, and as technology changed and factories closed, the black migrants from the South suffered. That is often the story we tell ourselves.

In testing this, Derenoncourt found the popular destination cities did not experience a faster loss of manufacturing jobs than other cities. Further, if the decline in upward mobility is explained by deindustrialization, it is peculiar that white men were not affected at all.

The real reason: The decline in upward mobility for black children, Derenoncourt maintains, is about how white local governments and residents in those cities responded to the migration. “Locations that received a lot of migrants started to reallocate spending toward police services,” Derenoncourt says. “They also experienced an increase in urban crime and incarceration rate." Great Migration destinations also saw an increase in white students’ enrollment in private schools and more white flight.

In the paper, Derenoncourt writes: “In response to millions of black migrants moving North to improve economic outcomes, receiving northern cities changed in ways that eventually shuttered this pathway to black economic progress.

Black families migrated north in search of opportunity, and the Northern cities responded with white flight and investment in police instead of schools. “It is the kind of tragic story where these locations that looked very good for black families, historically, today they rank lowest among places to grow up as a black child.”

What does this matter to Philadelphia? Philadelphia has about the same number of poor black residents as the entire population of Birmingham, Ala. To lift people and communities out of poverty, it is critical to understand the mechanisms that led to where we are today. "It’s not the soil or the air that makes a location good for upward mobility, but the decisions of local residents and local governments.” Neither poverty, school segregation, nor mass incarceration are acts of God. They are policy choices. Instead of trying to move children to different areas, we should identify bad policies, and work to reverse their damage.

“Brain Trust” is a new biweekly column that looks at how new research affects Philly. Ideas? Suggestions? Email Abraham Gutman at