Abstract

Debates about the medium of instruction in Nigeria tend to focus more on which language schools should use than on how competent learners are in the chosen language. The 2022 National Language Policy prescribed the mother tongue through primary school. Recently, in November 2025, it was cancelled in favour of English at every educational level. This conceptual paper argues that both positions leave a prior question unanswered: what spoken-language resources must learners have, or be helped to build, in whichever language carries instruction? The paper brings together the Simple View of Reading, Psycholinguistic Grain Size Theory and the Not-So-Simple View of Writing to show that spoken language is a continuing resource for reading, spelling, writing and comprehension. The resulting proposition is examined against research on second-language learners and African classrooms. Children taught in an additional language decode almost as well as their first-language peers, but they fall well behind in language comprehension. First-language vocabulary and grammar are only weakly related to those of the second language. In many Nigerian classrooms, the gap is visible in practice, where teachers use two languages throughout primary school regardless of policy. The paper therefore concludes that language choice and language development are separate decisions. It also argues that, until a medium-of-instruction policy specifies how oral language in the chosen medium will be developed, the policy is incomplete. Implications are drawn for policy, teacher education, classroom practice and assessment.