Cognitive flexibility, defined as the ability to adapt mental strategies to changing task demands, is fundamental to mathematical learning, particularly within the Moroccan primary school context where cognitive and demographic factors interact in complex ways. This study investigated the predictive role of cognitive flexibility in mathematical achievement, with gender and age examined as potential moderators. The participants were 60 fifth- and sixth-grade pupils (30 boys and 30 girls) without diagnosed learning difficulties. Data were obtained using the New Card Sorting Test (NCST) and mathematics grades, and were analyzed in R through descriptive statistics, correlation tests, t-tests, Kruskal–Wallis tests, and multiple regression models. The results indicated moderate mathematical achievement and a significant positive association between cognitive flexibility and mathematical performance. Gender exerted a moderating effect, with boys outperforming girls, whereas the age effect was non-significant. These findings suggest that cognitive flexibility contributes meaningfully to individual differences in mathematics learning. Strengthening this ability, especially among girls, could enhance problem-solving, adaptive reasoning, and overall achievement. Integrating cognitive flexibility training within mathematics curricula may therefore promote more equitable and effective learning outcomes in Moroccan primary education. Keywords: cognitive flexibility, mathematical performance, gender, age, new card sorting test