Wow... (In manga) I think that it's be okay for a boy to go to an all girl school but for a girl to go to an all boy school it'd be unhealthy...
Well when I say 'I think' it may be with the pov of a Japanese... which I don't have as I'm French
Anyway, I don't really know how to explain it but as : it's okay for a boy because it can lead to ecchi scenes but for the reverse it's sounds a bit twisted... :/