Have you found anything that speaks to single-sex education in western countries as better, or worse for girls, or boys?
Gender-segregated parochial schools in the US tend to have typical outcomes for boys and notably good outcomes for girls. (at least back when I was a student in the early 90s)
So single-sex education might be good for girls in America, but not for boys?
That was the case, at least for parochial schools in the 90s.