To develop human capital in the globalized world, governments have implemented policies that require the teaching of some or all school subjects in English. However, the implementation of this policy has faced criticism and challenges in some countries where linguistic and cultural diversity is prevalent. These challenges include school segregation based on the medium of instruction, inadequate English proficiency of teachers and students and less interaction in English Medium of Instruction classrooms. Some researchers have investigated these challenges through international assessments such as the Programme for International Student Assessment and Trends in International Mathematics and Science Study. Others have examined EMI mathematics and science classrooms qualitatively through observations and interviews. These studies showed that teachers and students are more comfortable, and the classroom environment is more interactive when they use their mother tongue. In general, the findings favoured the mother tongue education for both cognitive and noncognitive variables. Researchers recommend either switching to EMI after achieving a certain level of English proficiency or providing language support for students who are already in EMI systems. Finally, a case study from Wales suggested that providing questions in both the mother tongue and English might mitigate unfair linguistic advantages in international assessments.