Objective: Measurement tools for children's foundational skills provide important insights towards the developmental mechanisms of these domains. This study examines the structure of sensorimotor, visuospatial processing (VP), executive function (EF) skills and their interrelationship. The NEPSY is a widely-used neuropsychological instrument, but while validated at the domain-level through classical test theory approaches, no studies have conducted in-depth item-level analyses on its structural and psychometric properties. Method: This study examined whether the designed structure of NEPSY is empirically supported by fitting unidimensional and multidimensional Item Response Theory models to item response data of early elementary students in the United States. A confirmatory factor analysis was also conducted to examine the factorial structure of the data. Results: Results provide empirical support to the factorial structure of NEPSY, both at the domain level and within the VP sub-domain. The results show that VP and EF are separate constructs and subtests within the VP domain can further be modelled as interrelated but distinct factors -- non-motor and motor-based processing. Conclusion: Our specific results support the theoretical stance that VP consists of multiple component skills that are distinct because they require different neurological processes. This multidimensional NEPSY model shares some structural commonalities with the Cattell-Horn-Carroll model.