At the K-12 levels, education is generally provided very locally. American neighborhoods are very segregated by race and income. Nobel Prize winner Thomas Schelling had a clever "tipping point" model of this where people don't want to be "too much" in the minority. The results from this model can lead to surprising levels of segregation.
Tim Harford explains Schelling's tipping point model in a two-minute YouTube video
Schelling's tipping point model as downloadable software
Schelling's tipping point model shown through "Second Life"
Bill Easterly doubts that people really display this sort of behavior.
However, Card, Mas, and Rothstein find some pretty impressive results, in graphs starting on page 39 of this paper.
For amusement: It's probably a good thing that the military didn't listen to Schelling during the Vietnam War.
Or maybe it's good they did?