Impact of Mother-Tongue Instruction on Academic Achievement of Primary School Pupils in Enugu State, Nigeria

Abstract

The language of instruction remains one of the most consequential, and least consistently implemented, determinants of learning outcomes in multilingual African education systems. Nigeria's National Policy on Education recommends the mother tongue or the language of the immediate environment as the medium of instruction in the first three years of primary schooling, with a planned transition to English thereafter. In practice, English dominates classrooms in Enugu State from the earliest grades, even though Igbo is the home language of the large majority of pupils. This study examined the impact of Igbo mother-tongue instruction on academic achievement and academic interest among Primary 4 pupils in public schools in Enugu State. A pretest-posttest nonequivalent control-group quasi-experimental design was used. The accessible population comprised 12,480 Primary 4 pupils in 96 public primary schools across six local government areas. Using Yamane's formula at a 5% margin of error and allowing for attrition, a sample of 420 pupils (210 experimental, 210 control) was drawn through multistage sampling from 12 intact classes in 12 schools. Experimental classes received eight weeks of instruction in mathematics and Basic Science through Igbo, with English used only for technical terms that lacked stable Igbo equivalents. Control classes received the same content through English only. Instruments included a 40-item Mathematics Achievement Test (KR-20 = .86), a 40-item Basic Science Achievement Test (KR-20 = .84), a 16-item Instructional Language Exposure Scale (α = .81), and a 20-item Academic Interest Inventory (α = .88). After attrition, 410 pupils (206 experimental, 204 control) provided complete data. Independent-samples t tests and ANCOVA, controlling for pretest scores, showed statistically significant advantages for mother-tongue instruction in mathematics, Cohen's d = 0.72, 95% CI [0.52, 0.92]; Basic Science, d = 0.62, 95% CI [0.42, 0.82]; and academic interest, d = 0.55, 95% CI [0.35, 0.74]. Gender did not moderate the treatment effect. The findings support Cummins's linguistic interdependence hypothesis and the threshold hypothesis and have direct implications for language-in-education policy in Enugu State and comparable Igbo-speaking contexts.