The study investigated the relationship between gender difference and students' mathematics achievement from the school. The sample of this study was from a public junior school selected by using the method of convenient sampling. A total of 2251 students' data was collected and analyzed. The study found that there was no significant difference between male and female student' school mathematic achievement. Second, students' mathematics achievements had significant difference among three school math tests from each grade. Third, male students' scores were higher than females in the high score group from seventh grade. Female students' scores were higher than males in the low score group from ninth grade.