Zusammenfassung:
We study how linguistic mismatch between students' home languages and the language of instruction shapes learning productivity in linguistically diverse societies. We develop a framework in which linguistic distance acts as a multiplicative tax on educational production and derive welfare-theoretic conditions for optimal language choice. We apply the framework to Philippine elementary schools during the 2009-2024 mother tongue-based multilingual education (MTB-MLE) reform, exploiting policy-induced variation in linguistic alignment using difference-in-differences and shift-share instrumental variables designs. We extend the Foster-Greer-Thorbecke family of deprivation measures, traditionally used to quantify income poverty, to network settings in order to capture spatial variations in degree of linguistic mismatch and estimate substantial school-based linguistic deprivation under a counterfactual pre-reform bilingual language regime, concentrated in non-Tagalog-predominant regions. We find that each unit of mismatch reduces achievement by 35-57% of potential, depending on curricular subject, yielding productivity losses comparable in magnitude to canonical estimates of spatial misallocation in firm production. Under a counterfactual pre-reform bilingual regime, an average student would have operated at 27-45% below learning potential, with losses concentrated in linguistically diverse regions. MTB-MLE reduced these losses by roughly twothirds nationally, though systematic deviations from optimal language choice leave substantial efficiency gains unrealized. The reform also increased student continuation rates by 9-12 percentage points but temporarily strained classroom capacity, reflecting general-equilibrium resource pressures when demand-side constraints are relaxed. Overall, the results show that language policy is a first-order determinant of educational efficiency in multilingual settings and that measuring the quality of linguistic matching, rather than policy adoption alone, is central to evaluating language-in-education reforms.