Project Summary/Abstract It is estimated that approximately 10% of individuals suffer from dyslexia, a neurobiological disorder characterized by difficulty with accurate and/or fluent word reading and spelling (International Dyslexia Association, 2002). Current best practices for reading intervention are able to help improve accuracy in reading, yet to date there is no effective intervention for improving reading fluency beyond improvements in accuracy (Wolf and Katzir-Cohen, 2001). Because of this, many individuals with dyslexia struggle with fluency throughout their lifetime. One of the main barriers to developing effective fluency interventions is a fundamental lacking in our understanding of what contributes to fluency development. The proposed project aims to investigate what contributes to individual differences in reading rate from a developmental (longitudinal) perspective. The primary goal of the first study is to test the hypothesis that asymmetric development in word and non-word reading accuracy contributes to individual differences in word reading speeds. Specifically, it is hypothesized that those who grow more in word reading compared to non-word reading from 1st to 4th grade will read slower on timed word reading in 4th grade after controlling for accuracy. This pattern of asymmetric development would suggest that children may be adding whole word representations (like sight words) without recognizing the accompanying smaller units in a word. This alternative developmental trajectory may contribute to slower reading rates. The second study aims to investigate this mechanism by investigating the non-word features and person characteristics that contribute to the probability of reading a non-word correct. Specifically, it is hypothesized that slower readers will rely more heavily on non-words to look similar to words that they know. Understanding what contributes to individual differences in reading rate after controlling for accuracy will provide a better foundational understanding of these individual differences as well as provide a basis for future research for the prevention and intervention in issues in fluency.