There is continuing interest in the identification of student and instructional factors associated with the mathematics achievement of students in Japan. The Trends in International Mathematics and Science Study (TIMSS) assessments have provided opportunities to examine factors associated with mathematics achievement. The purpose of this study was to investigate relationships between confidence in mathematics and algebra test scores for eighth-grade students in Japan using data from the TIMSS 2011 assessment. There were a number of significant results from this study. Students who showed high levels of algebra achievement tended to indicate that they usually did well in mathematics and learned things quickly in mathematics. Similarly, students who felt they were good at working out difficult problems tended to show high test scores. Conversely, students who reported negative comparisons of themselves to their classmates tended to earn lower test scores. These findings indicate that it is important to consider student confidence in mathematics when assessing factors associated with algebra achievement.