Pennsylvania (1850) were the first medical institutions in the world established to train women in medicine and offer them the M.D. degree. During the 19th century, ideas about education started to change: modern ideas that defined education as a right, rather than as a privilege available only to a small elite, started to gain support in North America and Europe. Mass elementary education was introduced, and more and more coeducational schools opened. Together with mass education, coeducation became standard in many places. Increased secularization in the 20th century also contributed to the acceptance of mixed sex education. In 1917 coeducation was mandated in the Soviet Union. According to Cornelius Riordan, "By the end of the nineteenth century, coeducation was all but universal in American elementary and secondary public schools (see Kolesnick, 1969; Bureau of Education, 1883; Butler, 1910; Riordan, 1990). Furthermore, by the end of the 20th century, this was largely true across the world. In the U.K., Australia, and Ireland, the tradition of single-sex education remained quite strong until the 1960s. The 1960s and 1970s were a period of intense social changes. Many anti-discrimination laws were passed during that era, such as the 1972 Title IX. Wiseman (2008) shows that by 2003, only a few countries globally have greater than one or two percent single-sex schools. But there are exceptions where the percent of single-sex schools exceeds 10 percent: Belgium, Chile, Singapore, the United Kingdom, Hong Kong, Israel, New Zealand, Australia, South Korea, and most Muslim nations. Recently, however, there has been a resurgence of interest in single-sex schools in modern societies across the globe, both in the public and private sector (Riordan, 2002)." Effects The topic of single-sex education is controversial. Advocates argue that it aids student outcomes such as test scores, graduation rates, and solutions to behavioral difficulties. Opponents, however, argue that evidence for such effects is inflated or non-existent and instead argue that such segregation can increase sexism and impairs the development of interpersonal skills. Advocates of single-sex education believe that there are persistent gender differences in how boys and girls learn and behave in educational settings and that such differences merit educating them separately. One version of this argument holds that male-female brain differences favor implementing gender-specific teaching methods, but such claims have not held up to rigorous scrutiny. In addition, supporters of single-sex education argue that by segregating the genders, students do not become