Single-sex education refers most generally to education at the elementary, secondary, or postsecondary level in which males or females attend school exclusively with members of their own sex. This report deals primarily with single-sex education at the elementary and secondary levels. Research in the United States on the question of whether public single-sex education might be beneficial to males, females or a subset of either group (particularly disadvantaged youths) has been limited. However, because there has been a resurgence of single-sex schools in the public sector, it was deemed appropriate to conduct a systematic review of single-sex education research. The following are the major research questions addressed by the systematic quantitative review: (1) Are single-sex schools more or less effective than coeducational schools in terms of concurrent, quantifiable academic accomplishments?; (2) Are single-sex schools more or less effective than coeducational schools in terms of long-term, quantifiable academic accomplishment?; (3) Are single-sex schools more or less effective than coeducational schools in terms of concurrent, quantifiable indicators of individual student adaptation and socioemotional development?; (4) Are single-sex schools more or less effective than coeducational schools in terms of long-term, quantifiable indicators of individual student adaptation and socioemotional development?; (5) Are single-sex schools more or less effective than coeducational schools in terms of addressing issues of procedural (e.g., classroom treatment) and outcome measures of gender inequity?; and (6) Are single-sex schools more or less effective than coeducational schools in terms of perceptual measures of the school climate or culture that may have an impact on performance? As in previous reviews, the results are equivocal. There is some support for the premise that single-sex schooling can be helpful, especially for certain outcomes related to academic achievement and more positive academic aspirations. For many outcomes, there is no evidence of either benefit or harm. There is limited support for the view that single-sex schooling may be harmful or that coeducational schooling is more beneficial for students. Appended are: (1) Quantitative Study Coding Guide; (2) Qualitative Study Coding Guide; (3) List of Quantitative Studies Excluded During Phase III; (4) Quantitative Coding Guide for All Studies; (5) Table of Study Outcomes for Boys; and (6) Table of Study Outcomes for Girls. (Contains 35 tables and 1 footnote.)