The aim of this study was to examine the effect of middle school mathematics teachers' self-efficacy and leadership styles on middle school students' mathematical achievements and attitude towards mathematics. In this study, the general survey method was employed and the research population was consisted of a total of 917, 5th grade students, 472 girls and 455 boys, picked across 10 middle schools in a central district of a province located in North-West Anatolia. In order to gather scientific data, scales such as Mathematics Attitude Scale, Teacher's Self-Efficacy Scale, and Mathematics Achievement Test were used. Teacher characteristics were divided into two categories which consist of two and three sub-categories respectively; autocratic and semi-democratic based on the Leadership Style Scale. And low, moderate, high level according to teachers' scores in the Self-Efficacy Scale. The data obtained were analysed in accordance with the objectives by means of frequency, percentage, arithmetic mean, standard deviation, t test, one-way variance analysis (Ancova). The significance level in statistical analyses was set at p<0.05. Consequently, whether the teachers displayed low or high leadership styles had no significant effect on the students' mathematical achievement and their attitude towards the subject. Teachers' self-efficacy for classroom management sub-scale was found to have an effect on the mathematical achievement of students. The self-efficacy level of teachers for student engagement does not have a significant effect on students' mathematical achievement. However, it was found that teachers' self-efficacy for instructional behaviour, classroom management and student management affected students' attitude towards mathematics. [Note: The page range (221-238) on the .pdf is incorrect. The correct page range is p221-287.]