A growing body of evidence suggests that physical activity through enhanced cardiorespiratory fitness (CRF) has positive effects on executive functions (EF) and scholastic performance. However, EF assessment remains challenging due to complexity of the construct they encompass. This thesis addressed two different research topics, albeit related, about EF during middle childhood. First, I applied structural equation modeling (SEM) to investigate the indirect role of EF in the relationship between CRF and school grades (chapter 2). Second, I addressed a more methodological question about the sensitivity of SEM-based EF models to EF operationalization (chapter 3). This methodological work shows that the choice of EF operationalization matters, and proposes a novel indicator, drift-rate, which showed better psychometric properties than traditional indicators (e.g., response time, or accuracy) to assess EF. This work enabled to re-analyze the data from the first chapter (chapter 4), providing new information about the indirect role of EF components.