This study aims to investigate whether student anxiety about the subject of mathematics has any effect on the achievement of middle-school students in Amman, Jordan. It also aims to investigate whether student gender plays a role. The study sample consists of 180 seventh grade students enrolled in Amman public schools during the 2018/2019 academic year. These are distributed into three levels of anxiety as displayed by the students: low, middle, and high. Then, math anxiety measurements are collected, the validity and reliability for which are verified. The results reveal that there are statistically-significant differences in achievement between the middle level of math anxiety and the two other extremes. It is found that middle anxiety level have a positive effect on achievement, whereas for low and high math anxiety levels, no differences in achievement are perceived. In addition, no statistically significant differences ([alpha] [less than or equal to] 0.01) were found between males and females with regards to math anxiety; and there is no interaction between the level of math anxiety and gender in achievement.