Dyslexia: a validation of the concept at two age levels.

The 144 participants were administered tasks with a demonstrated relationship to reading. Both older students (8 to 10 years old) and younger students (6 to 7 years old) included three groups of poor readers (matched on word reading but differing in the discrepancy from expected reading level) and age-matched average readers. Older poor readers also had a control group of reading-matched younger subjects. The study provided no support for the concept of dyslexia at age 6 to 7 years. Among older participants there was support for the concept of dyslexia as a phonological deficit and of nondiscrepant garden-variety poor reading as a developmental lag. More discrepant participants with dyslexia exhibited orthographic and serial naming-speed deficits, as well as phonological deficits, and were a distinctive dyslexic group. Less discrepant participants with dyslexia were more similar to garden-variety poor readers than to the more discrepant participants with dyslexia.