This study is intended to examine the correlation between working memory of students and their academic performance in Mathematics. Specifically, it was aimed to determine the degree of relationship between working memory capacity and academic achievement of students in mathematics studying at secondary school. A sample of 800 students studying in grade 10 was randomly selected from forty government and private secondary schools (girls and boys) situated in Hazara division, Khyber Pakhtunkhwa, Pakistan. Both Urdu and English mediums of instruction schools were included in the sample. The researcher used digits span backwards test (DSBT) to find out the working memory capacity of the students associated with their academic performance in mathematics. This study revealed that girls have outperformed boys very markedly in examination scores of mathematics at secondary level. Contrarily, boys have performed well in working memory capacity than girls at the secondary level. However a very small gender difference is observed in this study. It is also noticed that private secondary schools showed higher performance in examination scores of mathematics and in working memory capacity than government secondary schoolsl.