IQ and reading progress: a test of the capacity notion of IQ.

Concepts such as developmental reading disorder and dyslexia have been used to refer to children whose actual reading achievement is substantially below that predicted by performance on IQ tests. Such diagnostic concepts assume that IQ sets a limit on either the level of achievement or the rate of progress of which a child is capable. This assumption was investigated in a longitudinal study of an unselected cohort of 741 children whose reading achievement was assessed at ages 7, 9, 11, and 13 years. Findings on rates of progress and levels of achievement clearly indicate that IQ does not set a limit on reading progress, even in extreme low IQ children. Thus, the use of IQ tests to determine achievement potential in reading appears unwarranted.