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Beyond horse race comparisons of national performance averages: math performance variation within and between classrooms in 38 countries

Reports of international studies of student achievement often receive public attention worldwide. However, this attention overly focuses on the national rankings of average student performance. To move beyond the simplistic comparison of national mean scores, this study investigates (a) country differences in the measures of variability as well as the measures of skewness and (b) the distribution of performance variability across schools and classrooms, employing data from the Trends in International Mathematics and Science Study (TIMSS) 1999. These findings reveal the stratification of student performance at the lower secondary school level in various educational systems, which has implications for both policy-making and research.