A connectionist model of reading development previously used to simulate detailed aspects of developmental dyslexia (Harm & Seidenberg, 1999) was used to explore why certain classes of interventions designed to overcome reading impairments are more effective than others. Previous research has shown that interventions targeting the development of spelling-sound correspondences are more effective at promoting generalization skills than ones designed solely to increase phonological awareness. The simulations broadly replicate the patterns of success and failure found in the developmental literature, and provide explicit computational insights into exactly why the interventions that include training on spelling-sound regularities are more effective than those targeting phonological development alone.