sexes. The number of public schools offering single-sex classrooms rose from 4 in 1998 to 540 in 2010, according to the web site of the National Association for Single Sex Public Education. Education Next and the Program on Education Policy and Governance at Harvard University sponsored a nationwide survey conducted by Knowledge Networks in early 2008. According to the survey, "more than one-third of Americans feel parents should have the option of sending their child to a single-sex school". Gender segregation in American history In the United States, gender segregation in schools was initially a product of an era when traditional gender roles categorically determined scholastic, professional, and social opportunities based on sex. For instance, leading experts supported gender segregation in higher education because they considered it "to be dangerous and inappropriate for women. Experts claimed that scientific evidence established that women were physically and temperamentally not suited to the rigors of the academy . ... Separate education for men and women paralleled the separate spheres that each was expected to occupy." Furthermore, colleges and universities did not consider female applicants until the second half of the nineteenth century, when the women's rights movement began advocating for gender equality. In response to social progression, "at the turn of the twentieth century, educators, particularly those in the South, fiercely resisted coeducation in elite all-male colleges, and most of the Ivy League institutions would drag their feet well into the twentieth century before becoming coeducational." Importance of history and culture in single-sex education determinations Girls and boys segregation in schools is definitive of a sex-based classification, and, thus, it must be supported by an "exceedingly persuasive justification" to pass constitutional muster. In light of this requisite standard, the legality of single-sex educational institutions depends on the accuracy of underlying assumptions and support. Accordingly, it is important to be aware that most research used to advocate the benefits of single-sex education is cloaked in uncertainty. Specifically, proponents "who want to build a case for single-sex education usually draw on ... uncontrolled studies, small samples, and anecdotal evidence; the positive findings are repeated but are not analyzed". Alternatively, opponents of single-sex education can gather tangible support from observable patterns of pervasive gender inequality in other social contexts. The diversity of opinions that concurrently support gender segregation in education creates a complex and fragmented dynamic. The miscellany of proponents includes: conservatives emphasizing innate gender differences,