The progress and prosperity of a country depends on the quality of mathematics taught in its school system. For people to survive and improve the quality of life, basic learning skills, reading, writing, arithmetic and life skills, are necessary and mathematics education is intended to develop these skills. The importance of mathematics transcends all definitions and no matter how much you ran away from the subject in school, mathematics, in daily life, chases you like a monster. No matter how hard you try, it is impossible to escape it. This study was done to see the relationship between mathematics achievement and reading comprehension and gender difference in mathematics achievement of children at upper primary stage. A sample of 307 upper primary children, 160 girls and 147 boys was taken through purposive convenient sampling method. Mathematics achievement test by N.C.E.R.T and reading comprehension test by Promila Pathak was used to collect the data. Mean, SD and t-test were used for the analysis of the data. Research findings revealed that Significant difference was found between mathematics achievement of girls and boys at upper primary school stage.Significant difference was found between reading comprehension of girls and boys at upper primary school stage.Significant positive correlation was found between mathematics achievement and reading comprehension of children at upper primary school stage.