THERE has been a flurry of activity in school choice research in the last few years. As a result, where we used to have only theories and limited evidence we now have a relatively solid understanding of the likely effects of school choice. I say “relatively” because all research is necessarily imperfect and additional study can always improve the confidence with which we draw conclusions.  But the research on school choice includes several randomassignment studies, the “gold-standard” of research design, where subjects are randomly assigned to treatment and control groups as in a medical study. I can think of only one other education policy issue (tile effect of class-size reduction) that has been the subject of even one significant random-assignment experiment, let alone several “gold-standard” studies.