Cross-language Transfer in Bilingual Children with Reading Difficulties: 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, less is known about how such cross-language effects unfold over time in children with reading difficulties. In a pre-registered, cross-over randomised controlled trial (registered on 23/09/2022; ID: 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 improvements in Welsh word reading at posttest, and children who received the intervention earlier showed advantages in Welsh at follow-up consistent with a timing-dependent effect. Short-term improvements were also observed in English decoding at posttest, providing evidence of cross-language transfer in this low-achieving sample. At follow-up, no between-group differences were observed in English. To our knowledge, this is the first randomised controlled trial to evaluate a literacy intervention delivered in Welsh, and the first to evaluate temporal effects on cross-language transfer in poorer readers. The findings highlight the importance of instructional timing and sequencing in bilingual literacy intervention.