Algebra knowledge is a critical part of middle-school mathematics achievement, and success in algebra is necessary for taking higher level mathematics courses and leads to higher scores on standardized tests. The purpose of this study was to simultaneously examine relationships between mathematics beliefs, classroom instructional strategies, and algebra achievement of adolescent students in the United States and Japan using data from the TIMSS 2003 assessment. Students from both countries who earned higher test scores were more likely to indicate positive beliefs in their mathematical ability, whereas students who earned lower test scores expressed negative comparisons of themselves to other students. Considering instructional practices, students who frequently worked problems on their own tended to earn higher test scores. These results indicate that students' mathematics beliefs and classroom instructional practices were significantly related to algebra achievement for students in the United States and Japan. (Contains 2 tables.)