Intelligence testing has a long and revered history in psychological measurement in childhood. Yet, the years between infancy and early childhood have been understudied with respect to emergent intellectual and cognitive functioning. Factor analytic models of intelligence that have demonstrated applicability when testing older children and adults often appear inadequate in the preschool period. As more is learned about brain development in typically developing children during these crucial years the distinctive relationships between neural system development and intellectual functioning are being revealed more completely. The aim of this paper was to provide a brief historical background as a foundation for discussion of intelligence testing, review what is known about the dynamic course of brain development during the preschool years, acknowledge limitations specific to intelligence testing in young children, and provide support for maintaining a comprehensive neuropsychological perspective that considers the wider range of variables that influence intellectual functioning in the preschool period.