This thesis focuses on the development of effective and sustainable policies that can support systems of basic education for children from minority ethnolinguistic communities in the complex multilingual context of the Philippines. The aim of the thesis is to identify, using a constructivist approach to grounded theory, the constraints and enablers of effective and sustainable mother tongue-based multilingual education for learners from minority ethnolinguistic communities, an approach which will enable learners to access quality education in multiple languages without sacrificing their own ethnolinguistic and cultural identity. Chapters 1 to 4 discuss the relevant literature associated with the context and subject focussing on the sociolinguistic and socio-historical issues underpinning language policy development and basic education in the Philippines. Chapters 5 and 6 situate Philippine realities within a broader international context reviewing the roles of international organisations as influencers of policy and implementation strategies. Chapter 7 considers the constructivist grounded theory and the rationale for the methodological approaches chosen for this research. This chapter outlines the research procedures and processes, data gathering methods and the limitations of the current research . This chapter also considers the role of the researcher as an outsider in a cross-cultural research environment Chapters 8 to 10 reviews data gathered during this research, organising and categorising responses and identifying themes. Chapter 8 describes the current realities in education for learners from minority ethnolinguistic communities in the Philippines while Chapter 9 outlines inhibitors and enablers of change as identified by respondents. Chapter 10 analyses the recommendations for change and development suggested by respondents. Chapter 11 contains conclusions and recommendations arising from the research. Recommendations include an increased need for evidential research on the impact of mother tongue-based multilingual education and improved awareness-raising and advocacy among influential stakeholders. There is a need to strengthen government capacity in the delivery of equitable education and also the empowerment of local communities to establish sustainable local education structures, responsive to local needs. Finally, this study recommends the implementation of rigorous systems for the monitoring and evaluation of mother tongue-based multilingual education programmes in order to identify effective practices