Educational productivity research has been a powerful tool to determine what affects students' academic achievement and to suggest effective educational investment for policy makers in both developed and developing countries. This research method has attempted to identify factors which influence educational achievement, treating school factors (e.g. teacher-pupil ratio, availability of educational resources, school management) as independent variables and treating educational achievement as a dependent variable. There has been small, but constantly reported, numbers of studies which identify significant difference between the findings of the educational productivity research from developed and developing countries. In this paper, first, I review some of the research on the differences and then argue why the differences occur between the two types of countries.