The study examined the effect of Gender and Social Economic Performance on Student Mathematics Performance. Data were from the Uganda National Examinations Board (UNEB) from the Primary Leaving Examinations (PLE) in the current academic year (n = 898). A Two-Factor ANCOVA was conducted to assess the effect of Sex (and SES) on student mathematics achievement controlling for mathematics pretest. The results indicate that there are significant differences between boys and girls on mathematics achievement controlling for prior mathematics ability. The adjusted means indicate that boys have higher mathematics achievement on average (M = 4.10, SE = .09) compared to girls (M = 4.61, SE = .12). Secondly, the pupils from higher SES (M = 3.38, SE = .14) have a higher math achievement as compared to their counterparts from low SES (M = 5.33, SE = .07). Note that the lower mean indicates better performance, and a higher mean indicates poorer performance on the PLE exams. (i.e., 1 is the highest score and 9 is the lowest score). These results seem to suggest the need to focus sex and poverty related interventions on students’ mathematics achievements.