Genetic and Environmental Influences on Prereading Skills and Early Reading and Spelling Development in the United States, Australia, and Scandinavia.

This study is a transnational and cross-linguistic study of twins that seeks to identify genetic and environmental factors that affect young children's language and literacy development. The study involves twins at daycare centres in Sweden, Norway, the US (Colorado) and Australia (Sydney area).

Comparison of averages revealed a significantly lower knowledge of written language at daycare centre level in Scandinavia, which is consistent with the relatively small amount of common reading and letter-related activities and the lack of focus on written language skills at Scandinavian daycare centres. OECD reports state that Scandinavian children are not inferior readers in later grades, which indicates that the life-related timing of instruction is not essential.

The study is a transnational and cross-linguistic study of twins and it includes a comparative analysis. The study involves 809 identical and fraternal twins of the same sex:  183 from Australia, 488 from the US and 138 from the Scandinavian countries. All the children had their respective national languages as their native language. 19 different tests were used to assess the children's language and literacy skills.

Samuelsson, S.; Olson, R.; Wadsworth, S.; Corley, R.; DeFries, J.C.; Willcutt, E.; Hulslander, J.; Byrne, B. (2007). Genetic and Environmental Influences on Prereading Skills and Early Reading and Spelling Development in the United States, Australia, and Scandinavia. Reading and Writing: An Interdisciplinary Journal, 20 (1-2), S. 51-75.