The emerging etiological model for developmental disorders, like dyslexia, is probabilistic and multifactorial while the prevailing cognitive model has been deterministic and often focused on a single cognitive cause, such as a phonological deficit as the cause of dyslexia. So there is a potential contradiction in our explanatory frameworks for understanding developmental disorders. This paper attempts to resolve this contradiction by presenting a multiple cognitive deficit model of developmental disorders. It describes how this model evolved out of our attempts to understand two comorbidities, those between dyslexia and attention deficit hyperactivity disorder (ADHD) and between dyslexia and speech sound disorder (SSD).