I went to a Catholic boys high school that was right next to a Catholic girls high school. The English classes were college level, the math as well. It really seemed to work. Plus, the two schools worked together on dances, proms, and all of the other stuff. Most of the kids from my class that I am still in touch with (men and women) have led very successful lives.
We had a similar situation in my Presbyterian high school -- our school was technically one school, but there was a Boys' School and a Girls' School. We had separate classes in everything but a few upper level courses where there weren't enough students to justify two classes - e.g. German IV and Computer Programming (in its primitive, PDP days . . . telling my age for those who remember stacks of punch cards and paper tape . . . ). Got together for dances, football games, etc. It seemed to work well.
I agree. I have friends that went to a Catholic all boys school, and their education is impressive. They were well into Calculus and Latin in their senior year.
I took one year of Calc myself as a senior in pulik skoo- that was the math ceiling for me. I think my brain still hurts sometimes. Newton was a sick dude to invent that.