Patrick Wolf of the University of Arkansas finds that private, charter, and magnet schools teach civic values as well or better than assigned public schools.

From the Education Next article:

In summary, the empirical studies to date counter the claims of school choice opponents that private schooling inherently and inevitably undermines the fostering of civic values. The statistical record suggests that private schooling and school choice often enhance the realization of the civic values that are central to a well-functioning democracy. This seems to be the case particularly among ethnic minorities (such as Latinos) in places with great ethnic diversity (such as New York City and Texas), and when Catholic schools are the schools of choice. Choice programs targeted to such constituencies seem to hold the greatest promise of enhancing the civic values of the next generation of American citizens.