There are many concerns around the recognition, development and use of local or minority languages in education. UNESCO believes that the issues of inclusion in education and quality education are closely related to a mother-tongue-based bilingual or multilingual education. While studies have shown that mother tongue matters for effective learning in education, few countries have introduced mother-tongue-based education programmes. The four case studies (Mali, Papua New Guinea, Peru and the United States) demonstrate the potential, benefits and challenges of a mother-tongue-based bilingual or multilingual education. This document aims to inform policy-makers on research evidence in mother tongue instruction and to raise their awareness regarding its importance. It will also serve to support policy decisions and policy-making at country level.