Interesting! I can definitely see both sides. As someone who went to an all-girls high school and loved the ability to focus and the lack of competition among the girls, I am a huge believer in them in that awkward age group. I am not sure I am so convinced in the younger years, however!
As a teacher, I can honestly say that when planning activities I strive to engage all of my students. There are some lessons that might be more interesting to the boys, while the girls might show more interest in other areas. However, I don’t necessarily see this as a reason to separate them in the younger years. As for older children, I think all boy/girl high schools are great. You are able to focus without trying to impress anyone else. I plan on sending both of my daughters to an all girl high school in my area.