The nation’s most segregating school district border divides Rochester from Penfield. In the 1950s and 60s, Rochester saw an influx of black residents seeking manufacturing jobs. Meanwhile, white city-dwellers began to leave for the suburbs. Penfield grew rapidly, and it took steps to safeguard its affluence. It essentially banned new construction of multi-family housing and set minimum sizes for homes and yards, a policy that would come to be known as “exclusionary zoning.” This put Penfield out of reach for lower-income families.

Meanwhile, Rochester’s manufacturing sector began to wane, leading to population decline and a decrease in fortunes. Trapped in a deteriorating city, poor Rochester residents filed a lawsuit challenging Penfield’s exclusionary zoning. In 1975, the Supreme Court found for Penfield. The ruling showed the way for communities that want to price out poorer residents. The border between the two school districts works in exactly the same way. The school finance system’s heavy reliance on local property taxes ties district budgets to home values, which means that when wealthier districts keep their walls up, they also keep property values high, local dollars in, and needy kids out.

For more on this border, see the long-form report here.

The fourth-largest poverty gap in the country is the 41-point divide between Claiborne and Hinds Counties in Mississippi. Claiborne needs more resources, not fewer, in order to properly support their high-need student body. But the district’s tax base is poor—not just because of low home prices, but because of state and federal actions taken with little concern for the Claiborne community.

In the early 1950s, a United States Army Corps of Engineers project had the side effect of flooding 657 acres of Claiborne County, destroying timber and devaluing the land. This takes a sizeable chunk out of the district’s property tax base each year. An even greater loss resulted when Mississippi exempted nuclear power plants from local property taxes—a 1986 change in law that affected just the state’s one and only nuclear plant, located in Claiborne County, almost immediately after it began operation. Meanwhile, other kinds of power plants continue to generate property tax revenue for their districts—districts whose populations are, on the whole, less needy than Claiborne’s.

While Claiborne struggles to fund its schools, Hinds County thrives. The district’s voters recently approved a $60 million bond to make updates and improvements to all its schools.

For more on this border, see the long-form report here.

The eighth-most segregating school district border is between Benton Harbor, Michigan and St. Joseph. Benton Harbor’s big industrial employer, Whirlpool, moved its factories overseas in 2010, after a long decline in local fortunes. Whirlpool still maintains a corporate headquarters locally, and its various nonprofit arms now buy and develop city land, taking advantage of government programs that are meant to spur investment.

One example is Harbor Shores, a luxury development supported by state tax breaks that are intended to aid projects in distressed areas. Parts of the development were set for St. Joseph, but construction in the more affluent town would not have been eligible for state assistance. To qualify, St. Joseph transferred some land into Benton Harbor. But once the tax breaks expire, that land, and the high-priced housing built on it, will go back to St. Joseph. This is a clear example of a wealthier community getting to have it both ways. The school district border walls St. Joseph off from Benton Harbor children, keeping its property values high and student poverty levels low. Yet when it was in St. Joseph’s interest, a border could be moved—to allow it to profit off the poverty of Benton Harbor.

For more on this border, see the long-form report here.

The country’s ninth-greatest school-district divide separates Clairton and West Jefferson Hills in Pennsylvania. Clairton is the rare story of an industrial town where the main employer has stayed—and the dependency of the local economy upon it has brought disastrous results.

Clairton Coke Works provides about a third of local tax dollars, but it also produces intense air pollution. Emissions got even worse recently as fires at the plant disabled air-quality controls. The numerous harms include a child asthma rate that is very high at 18%, well above the rate for Pennsylvania overall. Still, Clairton needs Coke Works. Union groups advocated against idling the plant despite the fires, and the mayor recently said that “If we closed that mill down…we’d be like a ghost town.” Leveraging its position, the plant’s owner reduced its tax bill by 40% on appeal. This is hard on Clairton, but the city cannot push back too forcefully when the alternative is nothing at all. The district needs those local funds; the state doesn’t even provide enough to bring Clairton up to parity with West Jefferson Hills. Meanwhile, Clairton faces the greater costs associated with serving its higher-need students, including providing school-based health services like asthma care.

West Jefferson Hills, though, has not had to make such hard choices about its local dollars. Residents have approved seven straight years of tax increases for schools and opened a brand- new high school this fall.

For more on this border, see the long-form report here.