The purpose of this study was to investigate the relationship between the sex of teachers and students and the students' achievement in mathematics, achievement motivation, and perceptions of teachers' leadership patterns. Two hundred and twelve student who took mathematics in the junior high schools were sampled. These students were divided into four groups: (1) 53 boys taught by male-teachers, (2) 53 girls taught by male-teachers, (3) 53 boys taught by female-teachers, (4) 53 girls taught by female-teachers. The instruments used were an achievement test in mathematics, a questionnaire of achievement motivation, and a questionnaire for the perceived leadership of teachers. The results were as follow: (1) Boys taught by male-teachers did better in mathematics than girls taught by male-teachers, whereas girls taught by female-teachers did better in mathematics than boys taught by female-teachers. (2) Boys' and girls' scores in achievement motivation were not related to sex of teachers, but girls obtained higher achievement motivation scores than the boys did. (3) Boys and girls had different perceptions of teachers' leadership patterns. Boys viewed that male teachers' leadership was more democratic than female-teachers'. On the contrary, girls perceived that female-teachers' leadership was more democratic than male-teachers'. They also thought that male-teachers' leadership was more laisserfaire than female-teachers'. However, all students said that male-teachers' leadership was more authoritarian than female-teachers'. (4) Boys were more inconsistant in their perceptions of female-teachers' leadership than their perceptions of male-teachers', while girls were more inconsistant in their perceptions of male-teachers' leadership than their perceptions of female-teachers'.