Cross-language Transfer in Bilingual Poorer Readers: Effects of a Literacy Intervention on Word Reading

Approximately 40% of children worldwide learn to read in a language other than their home language or in two languages simultaneously. Although literacy instruction in one language can enhance reading outcomes in another, the durability of these cross-language effects in children with reading difficulties remains unclear. In a randomised controlled trial, registered prospectively on 23/09/2022: https://www.isrctn.com/ISRCTN10963572 we evaluated a 15-week Welsh-language literacy intervention in 257 bilingual children with poor reading skills. Initially, 129 children (mean age = 111.44 months, SD = 12.23) received the intervention, while 128 (mean age = 110.62 months, SD = 12.34) served as a waitlist control. Reading efficiency in Welsh and English was assessed at baseline (t1), post-intervention (t2), and follow-up (t3; ~3 months later). The intervention produced significant and sustained improvements in Welsh word reading, Short-term improvements were also observed in English decoding, providing evidence of cross-language transfer, though these effects diminished over time. To our knowledge, this is the first randomised controlled trial to evaluate a literacy intervention delivered in Welsh, and provides evidence of cross-linguistic transfer in a minority-language context. Overall, a structured monolingual intervention in Welsh supported durable gains in the trained language and short-term gains in English. This highlights both the potential and the limits of cross-linguistic transfer and suggests that follow-up support may be needed to sustain gains in the untrained language.