I have heard that children attending a same sex school supposedly have less distractions, so they can focus on their studies. But school should not be just about academic success, it should be about teaching kids how to interact with all kinds of people and especially those of the opposite sex. Learning social interaction is an important life skill and I think school is the perfect environment. I would never consider sending my son to a same sex school.
I think a same sex school is not good for a child's development. While people can argue all they want about the supposedly lack of distraction, this is not necessarily true. Even in same sex school, you can still find the existence of social hierarchy, conflicts, or even bullying. If anything, same sex school makes the kids seem more naive and less prepared to deal with the opposite sex. Since most same sex schools are also boarding schools, kids learn about the opposite sex remotely from books or movies, which might give them a false impression. That is not to say some other issues could arise in such environment, e.g. homosexuality.
In response to the question I can only speak of my experience at a co-ed primary school and an all girls secondary school.
Looking retrospectively at my friendship group, it is clear that the same sex experience has benefited some whilst not being so great for others. Just as every child has a learning style, whether it be visual or aural etc, so are students in need of an environment that is conducive to their potential.
I myself enjoyed feeling comfortable conducting science experiments, not to mention doing sports with the same concerns as 99% of my peers... girls and our swimming woes.
Personally, same sex for secondary worked for my natural way of learning, however my sociability with males was unaffected due to my hobbies and interactions outside the strict school environment. In fact, most of my friends to this day are male!
Boys and girls learn in different ways, which is why boys have often lagged when it comes to exam results. Schools tend to teach in a way that girls are more engaged with. With same sex schools, they can be taught in ways that are more useful for them. But as Ivana said, you need to learn to socialise with the opposite sex too, so mixed classes are also good.
I was schooled at the leading Girls' School in this city, Grades 1>12. Had a marvellous 'career' there, both Academically, & Sporting.
Each of my children went to local State School, co-ed, Grades 1>4 inclusive.
Then Grades 5>12, to same sex Schools', both 'top-notch', with exceptionally high Academic achievement.
Both children enjoyed, & did very well. Both have gone onto professional working lives.
Son has several Qualifications', including B Hosp Mgt., & daughter, B Fin Plan & M Fin Plan.
So, for my family, the answer is a very happy 'yes'!