Why theories about developmental dyslexia require developmental designs.

This article examines the importance of developmental designs in dyslexia research using a neuroconstructivist framework. According to neuroconstructivism, the lowest level of impairment should be identified as early as possible, and developmental effects on higher-level cognition examined longitudinally. A number of recent studies proposing candidate low-level impairments have not used such developmental designs. The role of normal variation in postulated causal factors on development is ignored, inadequate control groups are used, and the nature and timing of environmental inputs are not measured, even though reading is taught systematically and both reading acquisition and dyslexia vary with orthography. It is suggested here that only a phonological deficit arising from low-level auditory processing problems meets the criteria for a neuroconstructivist approach.