The most segregating school district border in the country separates Detroit and Grosse Pointe, two municipalities with a long history of inequality. The 1974 Supreme Court case Milliken v. Bradley dealt with a desegregation plan that included majority-black Detroit and its nearly all-white, suburban neighbor districts, Grosse Pointe among them. In that case, the Court held that desegregation could not be ordered across the school district lines drawn by state and local governments. In essence, the Court declared school district borders to be impenetrable, even when cross-district efforts are necessary to achieve meaningful integration.

When the case was filed in 1970, the poverty rate among all residents of Grosse Pointe was 3%. Detroit’s poverty rate was five times that. Things have only worsened since; Detroit’s poverty rate is now 7.5 times Grosse Pointe’s.

The fact that the Detroit/Grosse Pointe border is the most segregating in the country is not surprising, but it is unfortunate. The legacy of the Supreme Court’s ruling in Milliken extends far beyond the school districts named in the case. Today, we contend with its impact not only in Detroit, but all across the country.

Jefferson County, and its central city of Birmingham, is a case study in gerrymandering. Birmingham is surrounded by 13 other school districts—almost triple the national average—with borders that zigzag through towns and around communities. Six of its borders are among the 50 most segregating in the country. The borders between Birmingham and two other districts, Vestavia Hills and Mountain Brook, are among the nation’s worst.

Both of these suburban districts seceded from Jefferson County, establishing wealthy enclaves that contrast starkly with neighboring Birmingham. While these districts have seen enrollments grow in recent decades, the departure of middle class families has left Birmingham with a smaller and poorer student body. In fact, its school-age population decreased 41% from 1995 to 2013, while its poverty rate increased by 13 percentage points.

Secession efforts are currently underway in many states and districts across the country. When communities are allowed to create their own, separate school districts, they can turn their backs on the poverty of their neighbors, creating economic segregation and significant disparities in resources.

The red dots represent the borders in the Birmingham area that are among the 50 most segregating in the country. Click them to explore.

Clairton and West Jefferson Hills school districts are just outside of Pittsburgh, in a region that suffered a significant decline in manufacturing jobs in the late 20th century. By 2010, unemployment in Clairton was 46% higher than the national rate.

West Jefferson, though, had been less reliant on manufacturing and fared well. Today, it has a healthy property tax base and can mostly self-fund its schools. Clairton, meanwhile, can only raise half as much from local taxes. That means that 71% of its resources must come from state “equalization aid.”

Throughout the country, low-income school districts rely on their states to supplement the dollars they can draw from meager property tax bases. Clairton is no exception. Pennsylvania, however, suspended its funding formula several years ago and cut its state education funding. Last winter, while Clairton was considering closing the district mid-year for lack of resources, West Jefferson approved construction of a $67.4 million high school.

In a system where low-income districts are the only ones dependent on the state to fully fund schools, it’s the neediest children who lose to politics.

Balsz Elementary School District serves students on the east side of Phoenix, just within the city limits. Wealthier Scottsdale Unified School District is in a suburb to its northeast. Their school-age poverty rates differ by a full 40 percentage points. The immense gap in their poverty rates is partly due to a sharp rise in Balsz’s immigrant population. In 1980, Balsz and Scottsdale had similar percentages of immigrant residents. By 2012, Scottsdale’s foreign-born population had doubled, but Balsz’s had more than quadrupled.

Since immigrants are more likely to be low-income than native-born individuals, it’s no surprise that during this period, the poverty rate among all Balsz residents increased almost threefold. Similarly, in 2014, less than one in ten of Scottsdale’s students were English learners, while in Balsz, almost half of students were. And despite the extra costs associated with providing services to these students, Balsz receives 30% less in state and local funding than Scottsdale.

Dayton, Ohio lost the majority of its manufacturing sector, and its middle class, by the end of the 20th century. Today, two of Dayton City School District’s borders—those with Beavercreek City and Oakwood City—are among America’s most segregating.

Ohio has an interdistrict enrollment program, permitting students to transfer to other districts—but only to those districts that elect to participate. Like many suburban districts bordering Ohio’s high-poverty cities, Beavercreek and Oakwood both decline to take part in the program. This means that Parkwood Elementary in Beavercreek is closed to Dayton students, though it is just a mile from the border. The school has a state grade of ‘A’ for its ability to reduce achievement gaps—exactly what’s needed for Dayton’s students, who are much poorer than those in Beavercreek.

Most states have interdistrict enrollment systems that include only select schools or districts. Open enrollment programs are attempts to work around the core problem of district borders, but they fall far short.