I went to Catholic schools from the age of 5 until I was 25 (except for periods when I was in the Army). Boys and girls in grade school didn't sit together but shared the same classrom, lines, etc. (bathrooms were also seperate). At the all-boys high school I took band, which was the only daily co-ed activity (hehehe). And college wasn't segregated at all, except for shower rooms and dorms and things, and maybe not even then.