In Germany, there are actually almost only mixed schools. Girls' or boys' schools are the exception rather than the rule and I personally don't know any more. When I was still at school 35 years ago, they still existed, but even then there were exceptions.
To be honest, I can't think of a single real reason why children should be separated by gender, only possibly by performance.
Separate genders only encourage unequal treatment of others. I also think that in some countries this method is only used to oppress women and steer them in a certain direction.
A state benefits from giving everyone the same opportunities, regardless of how rich or poor, male or female, or what color their skin is.
!BEER