Education

Here's an article that suggests that the more homogeneous the student body, the better the results. I was already familiar with the phenomenon here in the form of all-girls or all-boys schools, but apparently the effect is fairly wide reaching. The sole exception to this is the Islamic schools, which, in spite of being single sex and single religion, fall at the bottom of the curve.

I suppose there's a limit to what you can teach with only one textbook.