ABSTRACT
From the earliest IEA studies to the present ones, researchers have been interested not only in describing student achievement and the differences in achievement both within and across countries, but also in understanding the reasons behind these differences. To place our generalizations within a proper context, the authors will first describe what IEA studies say about the relative contributions of home and school to student achievement. While the IEA studies shed some light on the reasons for the strength of the relationship between home and achievement, they yield no evidence that would deny that relationship. The relationship between teacher knowledge and student achievement is supported by several of the IEA studies. For example, the IEA studies produced no evidence that increasing the number of hours per year spent on the study of a subject produces an increase in achievement.
