Mixed schools and segregation equilibrium

A recent article about Charter Schools in the US is a reflection of a long and continuing debate about how schools should be organized in multi-cultural societies. Integrationists favour mixed schools, where people from across the social and cultural spectrum, study in a mixed school. Segregationsists favour separate schools for each racial or social category, on the grounds that it provides the best opportunity for the racially, socially, or economically under-privileged to develop and sustain both (original and immigrant) their identities.

Charter Schools are publicly financed but independently conceived with the objective of improving academic performance and with curriculum similar to that of other public schools. Over the years, immigrant families, have come to see them as havens where their children are shielded from the American youth culture that pervades large public school district schools and where they can freely exercise their cultural identity. The article sums up the debate thus,

"Critics argue that these kinds of charter schools are contributing to a growing re-segregation of public education, and that they run counter to the long-held idea of public schools as the primary institution of the so-called 'melting pot', the engine that forges a common American identity among immigrants from many countries...

But... the reality is that most new immigrants become isolated in public schools, and that large numbers of them become alienated over time and fail to graduate... what these parents are doing, in taking ownership of their children’s schools, is as American as apple pie. They’re doing what soccer moms and dads in Lexington, Mass., and Concord and Cambridge do day in and day out. They’re modeling for kids the story of acculturation and how it works."

This debate takes us back to the Schelling chessboard experiment and its implications for emergent phenomena of segregation in schools - both racially and in the quality of students. It is now widely acknowledged that it is impossible to create stable and economically and racially mixed groups - schools or neighbourhoods. A number of models have all concluded that a mixed racial composition is inherently unstable and the only stable equilibria are fully segregated ones.

Update 1
Felix Salmon and Matt Yglesias points to the negative externalities generated by private schools in drawing away the better students thereby leaving the public schools impoverished. He therefore questions the equating such schools with charitable institutions and giving them tax concessions. In view of this, Free Exchange proposes taxing them for creating this negative externality.