(To answer your question an old study indicated that girls and boys benefit from having girls in the classroom. All girl classes tend to encourage girls but all boy classrooms tend to be very messy, and sloppy. All boy classes tend to get more hierarchical and bullying behavior increases. Discipline becomes more of a problem without girls in the classroom. But I understand some more recent studies showed all boy classrooms didn't always turn out bad. I'll look for the studies.)
But I have serious doubts that the segregation of the sexes is being promoted for the benefit of the girls. The religiously insane are doing it to keep the girls in their place. It really bothers me this separate but equal crap that quickly degenerates to separate but not equal.
From a feminist web site:
"Sure, some studies have shown that both girls and boys can benefit from being in a sex-segregated learning environment. But the right-wingers who are pushing for more single-sex schools don't have these benefits in mind. This is more of a tool to reinforce traditional gender roles than it is to improve learning.
Brad illustrates this with a great quote from the ACLU's complaint (PDF) against sex-segregated schools in Louisiana:
"Mr. Murphy briefly outlined the differences in instruction that would be given to girls and to boys. For instance, girls would receive character education and be subject to high expectations both academically and socially. Girls would be taught math through "hands-on" approaches. Field trips, physical movement, and multisensory strategies would be incorporated into girls' classes. Girls would act as mentors for elementary school girls.
On the other hand, boys' teachers would teach and discuss "heroic" behavior and ideas "that show adolescents what it means to truly 'be a man.' Boys' classes would include consistently applied discipline systems and offer tension release strategies. Boys' classes would also feature more group assignments."
So be very careful about these "same-sex" classes, they are a breeding ground for forcing gender stereotyped roles on children.
http://feministing.com/archives/005936.html