I read a great book a few months ago entitled "Why Gender Matters" by Leonard Sax (2005). It's subtitle is "What parents and teachers need to know about the merging science of sex differences". I tried writing a book summary in my wiki but I haven't got around to finishing it.
It makes a very strong case for single sex education by summarizing lots of research about the fundamental differences between boys and girls and how they learn and behave. It's a fascinating read. For example, there's a significant difference between the balance of M cells and P cells in the visual cortex of boys and girls. Supposedly, this gives boys the advantage in seeing movement while girls have the advantage in object discrimination. The author goes further by claiming that young girls draw nouns prefering warm colours while young boys draw verbs prefering cold colours.
There are many, many more differences which all lend a lot of weight to the proposition that the teaching style should be different for the two genders. The key point is that while you want both boys and girls to have the same opportunities, how each gender is engaged should be different. I gather this is a hot topic in education circles.
Since reading the book, I've raised the topic of single sex education in various conversations and there seems to be two main objections:
1) If you don't socialise boys and girls together, they tend to see the opposite sex as another species. You get even worse "boy crazy"/"girl crazy" behaviour in the teenage years. This is particular worse if a child doesn't have a sibing of the opposite gender.
2) In class discussions, the opposite gender will often bring up points of view that would not arise if the class was all one gender.
I guess the ideal compromise would be to have a mixed school with more single sex lessons that just P.E.. However, this has a taint of discrimination and stereotyping so I don't see how this could work in practice.
It's a pertinent topic to me since we need to start considering what senior school R* will attend and there's an all-girls school and mixed school close to us. It's a few years until we have to choose but it is on my mind.