Introduction: Differences in learning mathematics between boys and girls are being controversial according to different studies. However, those divergences are not always supported by empirical studies. One of the specific sources of difficulties on this topic is the fluency calculation learning, where performance differences between boys and girls need be clarified by new research, in order to gain more differentiated insights in possibly emerging gender differ, because the social and gender consequences. The current study analysed the gender differences in fluency calculation. Method: Participants were students of second cycle of primary education (n = 138), aged from 101-133 months old (8 year and 4 months to 11 year). Participants were 50 girls and 88 boys. Results: Statistical analyses did not showed differences between boys and girls in the 3rd grade of primary education. However, in the 4th grade the differences did reveal significant differences in the fluency calculation task. These results were supported by effect size and mutivariant analysis calculation. Discussion and Conclusion: Data suggests a gender gap around aged 9 between boys and girls, that would benefit boys in fluency calculation scores. Results, limitations and future potential research of the topic are discussed.