No teacher, however capable, can efficiently cope with the huge differences in academic preparation among the students in a typical American classroom—differences that grow with each successive grade.4 (In other nations, the differences between groups diminish over time, so that they are closer together by grade seven than they were in grade four. This effect has been most fully documented in European nations by the Organization for Economic Cooperation and Development, and among these nations, the most detailed data come from France.5)
This is a compelling datapoint.
