Modern behavior-genetic studies of twins in the United States, Australia, Scandinavia, and the United Kingdom show that genes account for most of the variance in children's reading ability by the end of the 1st year of formal reading instruction. Strong genetic influence continues across the grades, though the relevant genes vary for reading words…

The Matthew effect is often used as a metaphor to describe a widening gap between good and poor readers over time. In this study we examined the development of individual differences in reading and cognitive functioning in children with reading difficulties and normal readers from Grades 1 to 3. Matthew effects were observed for individual…

Genetic and environmental relations between vocabulary and reading skills were explored longitudinally from preschool through Grades 2 and 4. At preschool there were strong shared-environment and weak genetic influences on both vocabulary and print knowledge but substantial differences in their source. Separation of etiology for vocabulary and…

Twin children from Australia, Scandinavia, and the United States were assessed for inattention, hyperactivity-impulsivity, and reading across the first 3 school years. Univariate behavior-genetic analyses indicated substantial heritability for all three variables in all years. Longitudinal analyses showed one genetic source operating across the…

The genetic factor structure of a range of learning measures was explored in twin children, recruited in preschool and followed to Grade 2 ("N"?=?2,084). Measures of orthographic learning and word reading were included in the analyses to determine how these patterned with the learning processes. An exploratory factor analysis of the…

The importance of cognitive and language skills on reading and spelling development were investigated in a cross-linguistic longitudinal study of 737 English-speaking children (US/Australia) and 169 Scandinavian children (Norway/Sweden) from preschool to Kindergarten and Grade 1. The results revealed that phonological awareness and print knowledge…

This case study describes a 25-year-old Swedish woman with hereditary moderate hearing loss since birth who acquired both sign language and spoken language in her early preschool years and reached normal developmental milestones in each. Analysis revealed that her speech reading expertise is associated with cognitive functions such as high…