Tiebout choice among districts is the most powerful marketforce in American public education. Naive estimates of its effects are biased by endogenous district formation. I derive instruments from the natural boundaries in a metropolitan area. My results suggest that metropolitan areas with greater Tiebout choice have more productive public schools and less private schooling. Little of the effect of Tiebout choice works through its effect on household sorting. This finding may be explained by another finding: students are equally segregated by school in metropolitan areas with greater and lesser degrees of
Tiebout choice among districts.