I would have loved an all girls school growing up because most of the boys that lived near me were trouble makers and a distraction in class. The girls mainly got along until the age of 12 when bullying began.
I went to an all-boys school. From the perspective of academic education it was great because for the most part we could focus on learning rather than impressing the girls in the class. From a social education perspective it really wasn't very good because it meant few opportunities to interact with girls. I knew several people who went to all-boys schools and who didn't have sisters or female cousins who found it hugely awkward trying to figure out how to interact with girls when they went to university.
Meh. I can see why it can work, in helping reduce the distraction of trying to flirt with/impress the other sex. But personally, I would have hated it, since I'm a tomboy and I don't relate well to other girls at all.
Gender only schools shouldn't be made mandatory. It should continue to be the choice of the parent. I can see that distraction could be decreased and students may be able to focus more.