An aim of research on bilingualism is to understand how the brain adapts to the use of more than one language. Although several important discoveries and insights about the consequences of bilingualism have been generated over the last several decades, concerns about replicability have narrowed the scope of inquiry and discussion to the…

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…