In a world where sexism is still a huge problem, it seems that forcing students into a monosexual environment would only contribute to stunting their social development even more. Compare, for example, the relative incidence of sexism in a heavily male field like programming or philosophy with the amount of sexism in a gender-integrated field like biology.

This idea of separating students by gender to increase performance is really treating them like little test-taking machines: students, by and large, do not choose to take gender-segregated courses unless their parents require it of them. They're human beings. They have a fundamental right to develop in a natural social environment. And, like it or not, schools provide a large proportion of a child's social interaction, which isn't going to change anytime soon.

But most importantly, any improvements are highly controversial and tend to disappear once researchers attempt to correct for confounding.

"The Pseudoscience of Single-sex Schooling", Halpern et al, Science 2011: http://womenstudies.wisc.edu/documents/ScienceSingle-sex09-2...

The most successful school systems in the world, in Northern Europe and East Asia, are all coeducational. There are also a whole lot of interventions that don't require such drastic measures. Cracked of all publications wrote a surprisingly well-researched article on the subject:

http://www.cracked.com/article_19254_5-surprisingly-easy-way...

Using a microphone and turning on the lights is a far less severe encroachment on students' freedom than, well, segregation. Seriously.