Estimating the impact of language of instruction in South African primary schools: A fixed effects approach

For many children around the world, access to higher education and the labour market depends on becoming fluent in a second language. This presents a challenge to education policy: when and how in the school programme should a transition to the second language occur? While a large theoretical literature exists, empirical evidence is limited by the difficulties inherent to measuring the causal effect of language of instruction. In South Africa, the majority of children do not speak English as their first language but are required to undertake their final school-leaving examinations in English. Most schools offer mother-tongue instruction in the first three grades of school and then transition to English as the language of instruction in the fourth grade. Some schools use English as the language of instruction from the first grade. In recent years a number of schools have changed their policy, thus creating within-school, cross-grade variation in the language of instruction received in the early grades. We use longitudinal data on school characteristics including language of instruction by grade, and student test score data for the population of South African primary schools. Simple OLS estimates suggest a positive correlation between English instruction in the first three grades and English performance in grades 4, 5 and 6. After including school fixed effects, which removes the confounding effects of selection into schools with different language policies, we find that mother tongue instruction in the early grades significantly improves English acquisition, as measured in grades 4, 5 and 6. The significance of this study is twofold. Firstly, it illustrates the power of school-fixed effects to estimate causal impacts of educational interventions. Secondly, it is the first South African study (and one of a very few international studies) to bring robust empirical evidence to the policy debate around language of instruction.