The standardization of the NEPSY-A Developmental Neuropsychological Assessment (Korkman, Kirk, & Kemp, 1998) provided an opportunity to study the effects of age across the age range 5 to 12 years. Test scores of 800 children on 20 subtests of NEPSY were analyzed. These measures are based on traditions of neuropsychological assessment and are thought to reflect attention and executive functions, language, sensorimotor functions, visuospatial functions, and memory and learning. The effects of age were very significant on all measures, confirming the developmental sensitivity of the NEPSY. The effects of age were more significant in the 5- to 8-year age range than in the 9- to 12-year range. Only performance on tasks of fluency and memory span for sentences showed significant age effects in the 10- to 12-year age range. This suggests that neurocognitive development is rapid in the 5- to 8-year age range and more moderate in the 9- to 12-year age range.