Although for most of the nation's history, coeducation has been the norm in public elementary and secondary school, recent years have marked an increasing interest in public single-sex education. The No Child Left Behind Act of 2001 (NCLB) authorized school districts to use local or innovative program funds to offer single-sex schools and classrooms consistent with applicable laws and the U.S. Department of Education has published amendments to the Title IX regulations to provide additional flexibility to implement single-sex programs. In anticipation of an increase in the number of public single-sex schools, the U.S. Department of Education contracted with RMC Research Corporation to conduct a descriptive study of existing single-sex public schools to consider: (1) What is currently known about the effects of single-sex schooling on student achievement and other outcomes; (2) What is known about the causes of those outcomes; (3) Characteristics of public single-sex schooling, including contextual, instructional, and behavioral practices unique to single-sex schools; (4) Perceived benefits or disadvantages associated with single-sex schooling; and (5) Appropriate studies, including research questions and methodology, that will advance the knowledge base in this field. The study includes a review of the literature available in 2004, a survey of public single-sex schools, and a preliminary exploratory observational study of a subsample of currently operating public single-sex schools. Reported findings include: (1) Mixed results, with some suggestions supporting the premise that single-sex schooling can be helpful; (2) Little evidence of substantive modifications to curricula to address the specific needs of either boys or girls; (3) Greater positive academic and behavioral interactions between teachers and students in the single-sex elementary and middle schools than in the comparison coed schools.; (4) Both principals and teachers believed that the main benefits of single-sex schooling are decreasing distractions to learning, and improving student achievement; (5) Teachers cited greater benefits of single-sex schooling for girls than for boys in 5 of 10 benefit categories; (6) In separate focus groups, both parents and students cited essentially the same benefits as the teachers and implied that they chose the single-sex school for these reasons; (7) Teachers in single-sex high schools rated problems with student behavior as less serious than teachers in coed schools, although the opposite was true in middle schools; there were no statistically significant differences between single-sex and coed school teachers' ratings of problems at the elementary school level; (8) Compared to students in the coeducational schools, students in elementary and middle single sex schools exhibited a greater sense of community, interacted more positively with one another, showed greater respect for their teachers, were less likely to initiate class disruptions, and demonstrated more positive student role modeling than students in the coed comparison schools (site visits did not include a coeducational comparison high school); and (9) The research team suggests that future research use prior empirical work (both qualitative and quantitative) to identify variables that should be measured and potentially used as statistical controls, and recommends that a longitudinal study will yield data to evaluate both the effects of any randomization failure and the relative effects of attending a single-sex school. Three appendices include: ((1) Supplementary Exhibits; (2) Site Visit Reports; and (3) Data Collection Instruments. (Contains 16 footnotes and 41 exhibits.