To explore whether equality of educational opportunities is a reality in US eighth grade mathematics classrooms, this paper utilizes data from US states and districts that participated in the 1999 TIMSS-R study. Analyses explore the relationship between classroom coverage of specific mathematics content and student achievement as measured by the TIMSS-R international mathematics scaled score. District/state level SES indicators demonstrated significant relationships with both the dependent variable of interest, mathematics achievement, and the classroom level measure of content coverage. A 3-level model demonstrated a significant effect of classroom content coverage on student achievement while controlling for student background at the student level and SES at all three levels, documenting significant differences in mathematics learning opportunities among US eighth grade classrooms. (Contains 9 figures, 5 tables, and 4 endnotes.)