Abstract
<p>Spelling in bilingual children requires navigating two orthographic systems that may compete as well as cooperate. Although bilingual language research demonstrates extensive cross-language co-activation, far less is known about how such dynamics shape spelling development. We investigated whether cross-linguistic influence in spelling – indexed by the extent to which children’s misspellings conformed to English-consistent versus Welsh-consistent phoneme–grapheme mappings – predicted literacy development in Welsh–English bilingual children. Across three studies involving 524 children aged approximately 7–11 years, we quantified the extent to which misspellings reflected sublexical mappings characteristic of English or Welsh orthography. In Study 1, longitudinal analyses of children in control groups showed that greater phonological plausibility under English-consistent mappings at baseline predicted greater growth in English spelling accuracy, whereas greater plausibility under Welsh-consistent mappings predicted slower growth. In Study 2, a Welsh-medium literacy intervention did not affect English spelling accuracy but strengthened Welsh-consistent mappings and improved English-consistent mappings among children with the weakest baseline skills. In Study 3, an English-medium intervention strengthened English-consistent mappings but did not alter Welsh-consistent mappings. Together, these findings suggest that bilingual spelling development involves increasing differentiation of language-specific sublexical mappings through experience. This differentiation appears to be shaped by instructional context and orthographic depth, such that increasing sensitivity to target-language mappings supports spelling growth, whereas persistent influence of non-target mappings may constrain it.</p>