Purpose: Variability in the timing of infant developmental milestones is poorly understood. We used a twin analysis to estimate genetic and environmental influences on motor development and activity levels in infancy. Method: Data were from the Gemini Study, a twin birth cohort of 2,402 families with twins born in the United Kingdom in 2007.…

Previous studies have shown that environmental influences on school science performance increase in importance from primary to secondary school. Here we assess for the first time the relationship between the science-learning environment and science performance using a genetically sensitive approach to investigate the aetiology of this link. 3000…

Variability in achievement across learners is a hallmark of second language (L2) learning, especially in academic-based learning. The Twins Early Development Study (TEDS), based on a large, population-representative sample in the United Kingdom, provides the first opportunity to examine individual differences in second language achievement in a…

We investigated for the first time the genetic and environmental aetiology behind scientific achievement in primary school children, with a special focus on possible aetiological differences for boys and girls. For a representative community sample of 2,602 twin pairs assessed at age nine years, scientific achievement in school was rated by…

A behavioral genetic analysis of general writing ability was conducted using teacher assessments based on UK National Curriculum criteria for a sample of 3296 same-sex pairs of 7-year-old twins. Writing was highly heritable within the normal range (0.66) and at the low extreme (0.70). Environmental influences were almost all non-shared, with…

Background: It is widely believed that there are reciprocal links between reading achievement and reading exposure: children who read more do better at reading, and reading achievement itself promotes reading. We tested the hypotheses that these links arise because children's genetically influenced reading performance is correlated with their…

Using a longitudinal, large-scale sample of British twins, we addressed the prediction of both cognitive abilities and behavioral adjustment from eight domains of environmental risk: minority status, socio-economic status, maternal medical factors, twin medical factors, maternal depression, chaos within the home environment, and parental feelings…