The major purpose of the study was to detennine Gender mathematics concepts' perception and its effects on academic perfonnance of students in selected primary schools in Kyamulibwa subcounty, Masaka district, Uganda. The specific objectives of the study were to investigate the relationship between girl's attitude and performance in mathematics, Investigate the relationship between teachers' attitudes and girls' perfonnance in mathematics, Detennine the relationship between the curriculum and perfotmance of girls in mathematics, Detennine the relationship between over crowded classes and perfonnance of girls in mathematics. The methods used for data collection were questionnaires to the pupils and interviews with the teachers. The study revealed that few girls enjoy mathematics because they think that mathematics is hard and meant for boys who are clever. The study found out that teachers attitude towards girls performance in mathematics also affected there performance.