the average number of students currently in school
the average quality of education in a country
the average years of schooling each person receives
the average number of schools in a country
I believe the answer is: the average years of schooling each person receives
From knowing the average years of schooling that people have before graduation, we could make a rough assumption on the academic ability that average students in a certain area have, and the socio-economic factors that might cause it.
