The picture span performance of developmental dyslexic teenagers (mean age 14 years 1 month) was compared to the picture span performance of both RA (mean age 9 years 0 month) and chronological age match controls (mean age 14 years 1 month). Three stimulus lists were manipulated for visual and phonological similarity. Findings indicated that all three groups showed a significant phonological similarity effect but only the dyslexic group showed a significant visual similarity effect. The presence of dual visual-verbal coding is postulated to be responsible for the ‘noisy’ encoding which others (e.g. Johnston and Anderson, 1998; Swan and Goswami, 1997) have suggested is a root cause of dyslexia. The results are discussed in terms of developmental deficits in the central executive of the working memory system.