This cross-sectional study investigated whether the relationship between aerobic fitness and academic performance was mediated by executive functioning.A total of 378 children (9-10 years old) from nine primary schools in Stavanger, Norway were included. The children's aerobic fitness was measured by a 10-minute interval-running test; executive function was tested by four cognitive tests (Stroop, Trail Making, Verbal Fluency and Backwards Digit Span). A composite score for executive functions was computed and used in analyses. Academic achievement in reading, mathematics and English was determined using Norwegian national standardized tests.Bivariate correlation analysis showed the following significant associations: mathematic achievement with executive functions (r=0.48, P=0.001), aerobic fitness with mathematics (r=0.13, P=0.012) and executive functions (r=0.17, P=0.001). A regression-based mediation analysis (PROCESS) with executive function as a mediator variable was conducted. Mediation analysis showed that the relationship between aerobic fitness and mathematic achievement was mediated by executive functions (P<0.001).Findings revealed an indirect effect of executive function on the positive relationship between aerobic fitness and mathematic achievement.