There is disagreement over whether all school subjects should be taught in English or whether students should study in their mother tongue. In my opinion, the mother tongue should be the main language of instruction, with English taught intensively as a separate subject.
Supporters of English-medium education argue that it gives students better international prospects. Graduates who can study and work in English have access to more universities and jobs, and much of the world's scientific and technical literature is published in this language. Learning every subject in English may also lead to greater fluency, since students use the language constantly rather than only during language lessons. Some schools in countries such as Malaysia and India have adopted this model for these reasons.
Others believe that students understand lessons better in their own language. Complex concepts in physics or history are difficult enough without the extra burden of a foreign vocabulary, and pupils with weaker English may fall behind or lose confidence and stop participating. Teaching in the national language also protects it, as it will continue to develop as a language of science and literature. There is, moreover, a risk of confusion when students switch between two languages without having a strong foundation in either. Many teachers themselves are not fully fluent in English, which can reduce the quality of lessons.
For these reasons, I favour teaching in the mother tongue, particularly in the early years, when understanding is the priority. English can be taught through high-quality lessons, and perhaps through some subjects in the later years of secondary school, once the students have built a sound basis.
In conclusion, English-medium schools can improve fluency and opportunities, but learning in the home language leads to better understanding and protects national culture, so it should remain the main approach.