The purpose of this study was to examine the effects of fifth-grade mathematics teachers' efficacy (MTE) on their students' mathematics self-efficacy (SMSE) and mathematical achievement (SMA) in classrooms. Two mathematics efficacy instruments were administered to 58 classes (i.e. 58 teachers and 1244 fifth-graders respectively) to gather data associated with SMA scores in school. Statistical analyses were applied to the obtained data. The findings revealed that MTE beliefs significantly influenced both SMSE and SMA. Additionally, SMSE had a mediative impact on the effect of MTE on SMA. Subsequent to a discussion of the findings, suggestions were proposed for further improvement of mathematics teachers' efficacy and, in turn, for enhancing fifth-graders' mathematics self-efficacy and mathematical achievement in the future.