This is the executive summary for the full report, "Crossing the Line: Segregation and Resource Inequality between America's School Districts." School funding debates in the United States tend to center on how much money school districts should receive, and through what policies and formulas. But they almost never focus on the district map, even though district borders do a great deal to determine the funding of each school system. School district boundaries don't just define the area where a certain group of children attends a given set of schools. They also determine the taxing jurisdiction that supports those schools with local property taxes. Big differences in property value can lead to large funding gaps, even between neighboring districts. This report looks at neighboring school systems and the borders that separate them. It examined 24,658 pairs of adjacent districts and measured the divides between them in two ways. First, to measure economic segregation between neighboring districts, it compared their poverty rates among school-aged children, and identified the 100 borders that mark the greatest differences in poverty rates. Second, it looked at the differences in racial composition between adjacent districts by comparing their percentages of enrolled students of color, and identified the 100 borders that create the greatest differences by this measure.