Moving Cross-Language Transfer from Hypothesis to Causal Evidence: Effects of First-Language reading Skills on Second-Language reading Development in Ghana.

This article investigates the causal effects of first language (L1) reading proficiency on second language (L2) reading development in multilingual Ghana, using an instrumental variable (IV) approach based on a randomized L1 reading intervention among 4,352 early-grade students. The study finds that L1 proficiency positively influences basic L2 skills such as letter–sound recognition, but this effect weakens for pseudoword decoding and becomes nonsignificant for oral reading fluency, indicating inconsistent cross-language transfer. These results suggest that while foundational L1 reading skills support early L2 decoding, higher-order reading abilities in L2 may require additional instructional scaffolding beyond L1 proficiency. The findings have implications for language-in-education policies in Ghana and similar multilingual low- and middle-income countries, highlighting the need for targeted bilingual pedagogy and further causal research on reading development across languages.