It is widely but not universally believed that dyslexia (however it is defined) has a neurobiological basis. Denckla and Rudel (1976b), for example, wrote: “in the past decade there has been growing recognition that children described as having ‘developmental dyslexia’ are heterogeneous both etiologically and clinically, although the consensus is that all suffer from some kind of neurologically based dysfunction affecting their ability to learn, spell, and write” (p. 1). More recently, Stanovich (1991) noted that “The typical ‘media dyslexic’ is almost always a very bright child who is deeply troubled in school because of a ‘glitch’ (assumed to be biologically based…) that prevents him or her from reading” (p. 10).