A new report by the Board of the American Council of Coeducational Schooling (ACCES), The Pseudoscience of Single Sex Schooling, recently published in Science magazine  reveals (pdf)  that “placing children in single-sex learning environments is ineffective, misguided and may actually have harmful effects on children.” This data comes at a time when the number of single-sex classrooms in the U.S. is growing.  There were only two single-sex public schools in the 1990s but today there are more than 500 public schools that either offer single-sex classes or that are entirely single-sex.
The popularity of single-sex schooling has grown partially because of misinformation spread by proponents of single sex public schooling that boys and girls should be taught separately because of differences in their brains.  One of their proponents, Leonard Sax, executive director of the National Association for Single Sex Public Education, relying on research on rats, claims that boys need to be stressed in order to learn and therefore they must must be taught in cold classrooms in aggressive, confrontational styles.  Girls, according to Sax, require quiet warm classrooms, where they can take off their shoes and cuddle in a blanket brought from home.
Dr. Diane F. Halpern, the lead author of the report and past president of the American Psychological Association who holds a chair in psychology at Claremont McKenna College in California, said in an interview with the New York Times that Sax’s logic is faulty. She stated,

“A loud, cold classroom where you toss balls around, like Dr. Sax thinks boys should have, might be great for some boys, and for some girls, but for some boys, it would be living hell”…She said that while girls are better readers and get better grades, and boys are more likely to have reading disabilities, that does not mean that educators should use the group average to design different classrooms. “It’s simply not true that boys and girls learn differently…”

Indeed, the report argues that not only is single-sex schooling ineffective at improving educational outcomes, but it is actually harmful. The report states that “sex-segregated education is deeply misguided and often justified by weak, cherry-picked or misconstrued scientific claims rather than by valid scientific evidence.” It argues that “single- sex education reduces opportunities for boys and girls to interact together, which serves to reinforce negative gender stereotyping.”
The report “calls on the Education Department to rescind its 2006 regulations weakening the Title IX prohibition against sex discrimination in education.” These regulations allow single-sex classrooms provided they are voluntary, the school believes single-sex education will provide a better education for students, and that “students have a substantially equal coeducational option.” 
The Women’s Law Project has fought against discrimination in education. To learn about our work to prevent single-sex classrooms, click here.