Japanese compulsory education had been praised because of its equality around the early 80s. However, since the third wave-educational reform that began in the 1980s and still persists, it has been pointed out that there are disparities between schools in terms of students' socioeconomic background and academic performance. Although there have been studies assessing relationships between students' family background and academic ability between types of schools (e.g., private and public), how the disparities emerge between schools has not been investigated with nationally representative data collected in Japan. This study therefore attempts to empirically provide evidence of disparities between schools in elementary and lower secondary education by analyzing an age cohort at two points of time. Using fourth grade data from "The Trends in International Mathematics and Science Study" (TIMSS) 2007 and eighth grade data from "TIMSS" 2011, the study first assesses (1) whether a school-composition of students' cultural capital (school-CC) shapes teachers' expectations for student achievement and (2) whether teachers' expectations relate to their teaching approach, which is measured as the frequency of homework assignments given to their students. After these two relationships are tested at the school level, the study investigates, through a multilevel regression analysis, (3) whether teachers' expectations and teaching approach are associated with students' academic performance in mathematics so as to reveal how school-CC-disparities relate to the achievement gap between schools. Findings of this study indicate disparities between schools in terms of school-CC, the degree of teachers' expectations, the frequency of homework assignments and math-achievement in eighth grade, while some disparities between schools are found at the fourth grade level. The findings also show that teachers' expectations are associated with eighth grade students' academic performance; that is, the degree of teachers' expectations partly explains the achievement gap between schools.