The relevance of medium of instruction and mother tongue for different types of educational systems

The relationship between student performance in education and medium of instruction needs to be investigated in a systems-oriented way, comparing what educational systems are able to achieve given different medium of instruction policies. This article combines data on language, medium of instruction, participation in education and effectiveness of education to propose a new categorization of educational systems: colonial systems, decolonial systems and systems in transition. It shows that there is an evolution towards decolonial systems, but that such an evolution will require a transition to indigenous languages as medium of instruction. It briefly discusses the pitfalls and possibilities of such a transition.