I'm going to c&p my post from another thread because I'm lazy, and it seems relevant here too:
Historically in the UK I would imagine that girls and boys were separated for reasons of propriety, because it was deemed somehow 'improper' that they should mix in case they were 'tempted'.
For sexual equality reasons, we have moved on from this now, so that we learn from a young age to deal with being in an environment with the opposite sex, since that after all is the real world - we aren't in Jane Austen times any more.
If it turns out that in the Birmingham schools girls and boys are not being separated for reasons of propriety, and that they are in fact being treated equally, in accordance with education guidelines and legislation, then that's all good.