This paper is in part an answer to the question posed in a recent issue of "Educational Researcher" by Goldhaber: "School choice: do we know enough?" It also summarizes the results on the relationship between school choice and social segregation in the United Kingdom. Data used in this paper come from several sources, including official statistics and interviews with local education authorities. School choice was substantially increased in 1988; the analysis is based on the entire United Kingdom student cohort and for every year between 1989 and 1999. A range of segregation measures were used, though the results are invariant to the index used. Socioeconomic stratification in all secondary schools in England declined from a high of 36 percent in 1989 to around 30 percent by 1996, but rose to 32 percent by 1999. There is no evidence that within this decline in stratification, a subset of schools went into a "spiral of decline." The decline in differences in attainment between social groups may be the result of market reforms having worked, or a result of a larger trend arising from the United Kingdom's history of continuous improvement and "comprehensivization" in schooling. Other possible factors are greater "equality in poverty" and school reorganizations. (Contains 38 references.) (RT)