The question of whether single-sex (SS) schooling is preferable to coeducation (CE) for some or all students continues to be hotly debated. Much of the debate is philosophical and would be waged even if single-sex schooling were shown to be highly advantageous for one or more subpopulations. However, the actual research evidence, although suggestive that SS schools can benefit some students in some realms of academic and socio-emotional accomplishment, is equivocal.

True randomized experiments in which students are randomly assigned to schools would be highly beneficial to this question. However, this would require significant social engineering and disruption of lives, making such studies almost impossible. In addition, correlational studies that control for all pre-existing differences between students attending the CE and SS schools could effectively address this question. However, the uncertainty about appropriate controls and the large amounts of data needed also make this research quite daunting. As a result of the obstacles to conducting such research, there have been few or no studies definitively showing evidence for or against SS schooling.

The primary purpose of this paper is to enumerate, categorize, and critique extant explanations for why SS schools should be more or less effective than CE schools, in what realms, and for what outcomes.