Writing ability is a fundamental educational skill that significantly
influences academic achievement and broader life outcomes. Despite its
crucial role, research investigating early predictors of writing
development remains limited compared to other literacy domains,
particularly regarding genetic and environmental contributions. Using the
dataset from the Twins Early Development Study (TEDS), this study
aims to investigate the longitudinal relationships between early
predictors, including cognitive and non-cognitive abilities (e.g. language
skills, motor skills, behavioural indices) assessed at ages 2, 3, 4, 4.5, and
writing outcomes, and a diagnoses of Specific Learning Disorders (SLD),
assessed at age 7, 9, 12. Specifically, we distinguish between
developmentally distal predictors, such as broad cognitive and language
skills assessed in infancy, and proximal predictors, more domain-specific
skills such as phonological awareness or early numeracy, assessed closer
to the time of formal literacy instruction. Using a twin-difference design,
accounting the genetic similarity of monozygotic and dizygotic twins, we
estimate the relative contribution of genetic, shared, and non-shared
environmental influences on writing development and SLD. Our findings
would contribute to understanding the developmental pathways leading
to writing difficulties and SLD, offering insights into early identification
and tailored intervention, informed by genetically sensitive methods.