Mother tongue-based education in a diverse society and the acquisition of foundational skills: Evidence from the Philippines

• Mother tongue-based education is considered effective in increasing learning outcomes. • The Philippines implemented a mother tongue-based education program in 2012. • We use a double-difference method and find a negative effect on reading skills. • The program also reduced foundational math skills among the first student cohort. • High linguistic diversity complicates mother tongue-based education implementation. The Philippines is an ethnolinguistically diverse country with 180 languages spoken. In 2012, the government massively expanded the language of instruction (LoI) options, a shift from a bilingual Filipino-English education to mother tongue-based education using 19 languages targeting students in kindergarten to grade 3. The policy intended to create a closer link between the school instructional language and students’ mother tongue in the early stage of formal schooling, which would improve foundational skills and increase the students’ ability to acquire proficiency in additional languages. We use nationally representative data to evaluate the policy's impact on foundational reading and mathematics skills, exploiting a variation between student cohorts and the variation in the instructional languages before and after the policy. We find that the policy reduced the mean linguistic distance between children's mother tongue and school LoI by between 43 % to 76 %. However, we find a statistically significant and negative effect on foundational reading skills when tested in Filipino or English. The magnitude is not negligible given the Philippines’ flat learning profiles. We find the policy also negatively impacted the foundational mathematics skills of the first cohort fully exposed to the policy. Our findings imply that governments need to reconsider the mother tongue-based education policy as a tool to improve foundational skills in a diverse society.