The purpose of this study was to examine the development of oral reading fluency in a sample of first-grade children. Using growth curve analysis, models of growth were identified for a combined sample of at-risk (AR) and not-at-risk (NAR) children, and predictors of growth were identified for the longitudinal AR sample in first and second grade. Large and serious differences in reading fluency growth between the AR and NAR samples were apparent early, replicating other reports. Theories of sight-word learning and reading fluency were supported, in that letter-sound fluency was a uniquely significant predictor of first-grade reading fluency. The effects of phonological awareness and rapid automatized naming were mediated by the other variables in the model. Growth in first-grade oral reading fluency accounted for the most unique variance in second-grade growth and end-of-year performance. The results suggest that word reading fluency should be regarded as developing concomitantly with early word recognition rather than as a later-developing skill.