My DDs current class is almost exactly 2/3 boys at this point. It's a private school that due to it's demographic attracts more boys than girls - people willing to pay the fees mostly believe boys should go co-ed and girls should go single sex. They send their sons to our school and their daughters to similar girls-only private schools near by.
Up until now we have been determined to send our girls co-ed because they have no brothers, but most of their close friends are boys. However, it seems like the school is really struggling to maintain their gender balance at the moment, which was already worrying me. Reading this thread has just brought up all my memories of being the "weird smart girl" in primary school and how badly that went down in a co-ed school. By the end of primary school I refused to go to school at all unless my parents found me an all girls school, of course retrospectively I was still weird and isolated, so I don't know if it helped.
My DD doesn't complain about the boys at school being dominant, so I haven't given it too much thought. Though I was pretty shocked at how separate the genders were at her birthday party last month and how poorly the boys behaved. It was certainly very different to how things have been in the past, leaving me wondering whether it's age related or whether her class is now too heavily biased towards boys.
How do you weigh an issue like this against a school otherwise being the ideal fit for your child. I honestly believe that the school has the best services and differentiation available in my city, perhaps there are one or two co-ed schools that may be equal but I don't think there are any better and as far as I am aware any of the others that are of a similar quality have the exact same issue maintaining balance. And all my reasons for wanting the co-ed remain, all girls might fix some issues but it introduces issues of it's own too.
Which is my long winded way of saying I understand your anxiety but have I no idea what to suggest.