Investigating the Double-Deficit Hypothesis in More and Less Transparent Orthographies: A Longitudinal Study from Preschool to Grade 2

We investigated the double-deficit hypothesis (DDH) in samples of U.S. (N = 489), Australian (N = 264), and Scandinavian (N = 293) children followed from preschool to grade 2. Children were assigned to double deficit, single deficit and no deficit subtypes in preschool, kindergarten, and grade 1 and compared on reading and spelling in grades 1 and 2. In most analyses, the double deficit subtype scored significantly lower in reading and spelling than the single deficits, a pattern of findings that was identical across samples. Moreover, across countries, RAN deficits showed a stronger effect on reading whereas PA deficits showed stronger effects on spelling. Overall, the results supported the basic premises of the DDH suggesting that the double deficit subtype represents the most impaired readers, and that RAN and PA are separable deficits with different effects on reading and spelling. The results also supported a universal view of literacy development, with similar predictive patterns of DDH subtypes across orthographies.