This study used the TIMSS 2011 International Database to investigate predictors of 8th-grade mathematics achievement across three countries that represent a wide range of cultures and levels of mathematics achievement: Chinese Taipei, Ghana, and the United States. A review of literature on predictors of mathematics achievement yielded variables in four major contexts of learning—a student’s home, beliefs, school, and classroom. The variables of home that were investigated are home possessions for learning, parent education, and parents’ expectations and involvement in their children’s education. The variables of student beliefs were self-confidence in mathematics and the value of mathematics. The variables of school were school climate, school resources, administrator leadership, and school socioeconomic status. Finally, the variables of the classroom are access and equity, curriculum, tools and technology, assessment, and teacher professionalism. A 2-level hierarchical linear model was used to investigate relationships between the predictors for learning mathematics and 8th-grade mathematics achievement. Level 1 represented the relationships among the student-level variables, and Level 2 represented the school-level variables. In Chinese Taipei, statistically significant predictors of mathematics achievement in the final model included variables from the domains of home resources, student beliefs, school climate, and school socioeconomic status. In Ghana, both student-beliefs variables had statistically significant relationships with mathematics achievement, and one school climate and one school socioeconomic status variable each was found statistically significant. The U.S. had statistically significant predictors in the domains of home resources, student beliefs, school socioeconomic status, classroom-level access and equity, classroom assessment, and teacher professionalism. This study extends previous research in several ways. It includes a review of classic and recent literature regarding predictors of mathematics achievement; 17 scales using the Rasch partial credit model were developed to measure predictors of mathematics achievement; and the results of this study may be used to examine the relationships between the independent variables of this study and middle-grades mathematics achievement in countries similar to the 3 in this study to reinforce and support variables that contribute to student achievement.