This report wants to know how many students would benefit from increased public-school choice, especially the kind that involves crossing the border between districts. Not too many, it finds. School capacity and driving distances limit options, even when students are permitted to cross district lines. The report also notes that, despite 46 states having some type of open-enrollment law, and 42 with inter-district choice, 80 to 90 percent of students in low-performing schools remain in them. Author Erin Dillon used Geographic Information Systems (GIS) mapping technology to discover high-performing schools within a 20-minute driving radius of a low-performing school. She assumed that the high-performing "receiving schools" could increase their capacity by 10 percent to accommodate transferring students. These limiting assumptions--20 minutes and 10 percent capacity--have been criticized as too conservative but Dillon herself explains that once travel time is expanded beyond 20 minutes, increased access and subsequent competition for spots in receiving schools negates any benefit. More interesting is how Dillon identifies her low- and high-performing schools. She rates them on a 1 to 5 scale, but labels them "high" and "low" performing based on how they compare to their neighboring schools, rather than on their absolute scores. To be labeled high-performing, a school has to be 2 quintiles above its low-performing counterpart; in other words, a school that by absolute standards is mediocre could be termed high-performing in Dillon's study. Seems reasonable. The overall lesson, though, is this: it's important to have other options, such as vouchers and charter schools, to supplement public-school choice. A copy can be found here.