An overwhelming body of research shows that coeducation is better for girls and boys.
"decades of research on academic outcomes from around the world has failed to demonstrate an advantage to single-sex schooling, in spite of popular belief to the contrary. Of course, there are some terrific single-sex schools out there. However, research finds that their success is not explained by gender composition, but by the characteristics of the entering students (such as economic background), by selection effects (for example, low performing students are not admitted, or are asked to leave), and by the substantial extra resources and mentoring these programs provide."http://www.slate.com/articles/double_x/doublex/2011/10/the_single_sex_school_myth_an_overwhelming_body_of_research_show.html