Emerging findings from genetic, neurological, and cognitive studies of dyslexia are beginning to provide researchers and educators unprecedented insights into the nature of reading failure. Converging interdisciplinary evidence supports a highly complex and multi-componential view of dyslexia--in marked contrast to single-deficit cognitive models that prevail in research and practice--suggesting the need for a dynamic developmental approach capable of characterizing the complex interactions among multiple biological, cognitive, and environmental factors. The shift in interdisciplinary research toward a more integrated and contextualized view of dyslexia, along with an explicit focus on the central importance of developmental factors, will likely have immediate implications for the way reading failure is characterized in adolescence. In this dissertation I present the findings from an individual-differences study of fluency in oral reading of connected text in 77 adolescents with dyslexia. The key finding from this study is that verbal short-term memory is a significant predictor of oral reading fluency in adolescents with dyslexia, but the magnitude of its effect changes greatly with amount of expressive vocabulary knowledge. Specifically, whereas the effect of verbal short-term memory on oral reading fluency is strongest with lower levels of vocabulary, it becomes much weaker with higher levels of vocabulary knowledge. These findings provide some support for the changing nature of dyslexic symptoms across development, and offer evidence in favor of a more dynamic developmental systems approach to the study of reading failure in adolescence.