Duncan et al. (2007) presented a new methodology for identifying kindergarten readiness factors and quantifying their importance by determining which of children's developing skills measured around kindergarten entrance would predict later reading and math achievement. The main objectives of this paper are threefold: (a) provide new empirical evidence that fine motor skills, a developmental skill measured at school entry but not included in Duncan's et al.'s (2007) analysis, is strongly predictive of later scores, (b) present several sensitivity analyses that extend Duncan et al.'s findings, including assessing the predictive power of a child's knowledge of the world, and (c) review the developmental, cognitive, and neuroscience literature to assess and suggest mechanisms for a link between early motor skills and later achievement. Three large scale longitudinal data sets are used in this study. They are the Early Childhood Longitudinal Survey- Kindergarten Cohort (ECLS-K), the British Birth Cohort Study (BCS), and the National Longitudinal Survey of Youth (NLSY). The results indicated that gross motor skills were not a significant predictor of later achievement but that fine motor skills were a very strong and consistent predictor of later achievement. A table is appended.