Reading development utilizes and repurposes multiple cognitive and neural systems that support innate functions such as vision, hearing, language, and learning. In most children, these systems become seamlessly integrated through the experience of reading to form a reading circuit. In a subset of children with developmental dyslexia, however, neural specialization for reading proceeds atypically and reading impairment ensues. Because of the complexity of this circuit and the heterogeneity of dyslexia-related deficits, forming a cohesive theory of dyslexia etiology has been challenging and multiple hypotheses have been proposed. To establish the etiological causes of dyslexia, it is important to demonstrate that a particular mechanism of deficit precedes reading impairment and is present in pre-reading children. This dissertation reports findings from four studies that investigated the cognitive, neural and environmental substrates of reading failure in pre-reading children. Specifically, Study 1 applied latent profile analysis to identify heterogeneous profiles of dyslexia risk in 1,215 kindergarten students and to demonstrate the high longitudinal stability of these profiles. Using voxel based morphometry and diffusion weighted imaging, Study 2 demonstrated the grey matter and white matter characteristics of each of the risk profiles identified in Study 1 in a subset of the children (n=100). The study also showed that some neuroanatomical substrates of risk predict longitudinal reading outcomes above behavioral measures. In support of the regularity extraction deficit in dyslexia, Study 3 demonstrated unique association between the processing of temporal regularity in musical rhythm and reading development in 74 kindergarten children. Furthermore, a mediation analysis revealed a causal path from rhythm performance to phonological awareness skills and to reading skills. Finally, using diffusion methods, Study 4 demonstrated links between socioeconomic status (SES) and the coherence of white matter tracts important for reading development. Additionally, SES modulated the relationship between dyslexia risk and longitudinal reading outcomes. The findings in these studies may contribute to a better theoretical understanding of the etiology of dyslexia and in addition, highlight the importance of early identification and individualized remediation.