International studies in education provide researchers with opportunities to examine how students with both similar and dissimilar formal education systems perform on a single test and provide rich information about the relationships among student outcomes and the factors that affect them. Using hierarchical linear regression techniques and TIMSS 1995 and 1999 data from 23 countries, this research examines the association between the structure of the environments within which students receive instruction and mathematics achievement. In addition, the relationship between background characteristics and 8th-grade mathematics achievement is explored.