Investigating the Relationship Between Yoruba Language Proficiency and Academic Performance in Osun State Secondary Schools

The relationship between first-language proficiency and academic performance across subjects is a foundational question in educational linguistics with significant implications for mother tongue instruction policy. This study investigates the relationship between Yoruba language proficiency and academic performance among senior secondary school students in Osun State, South West Nigeria. Using a quantitative correlational design, data were collected from 300 Senior Secondary 2 students across 15 schools in Osogbo, Ede, and Ilesha, drawing on Yoruba language proficiency test scores, WAEC subject grade records, and teacher-rated academic performance assessments. Yoruba proficiency was measured across reading, writing, listening, and speaking dimensions using a validated instrument adapted from the Nigerian Standard Yoruba Proficiency Framework. The study applies linguistic interdependence theory and Cummins' common underlying proficiency hypothesis as its theoretical framework. Existing literature on language and academic performance in Nigeria has predominantly examined English proficiency, with Yoruba proficiency as an independent academic variable being insufficiently studied in a multisubject context. This study addresses that evidence gap with empirical correlational data. The research examines whether Yoruba proficiency correlates positively with performance in Yoruba-medium subjects and whether there is evidence of cross-linguistic transfer benefiting performance in English and other subjects. Findings are expected to demonstrate a significant positive relationship between Yoruba proficiency and academic performance across multiple subject areas. Recommendations will address mother tongue instruction policy and support for Yoruba language development in Osun State schools. Keywords: Yoruba proficiency, academic performance, secondary schools, Osun State, linguistic interdependence.