MOI is a big issue in Hong Kong, and also in some multi-lingual countries such as Singapore. But it is not an issue in other places, where there is only one daily language, not necessary English. I read a scientific paper on language and the process of consciousness. It said language is the key to human consciousness. The development of complex language distinguishes modern human being from the ancestral humanoid. The theory is that babies develop their consciousness through communicating with parents. The language ability in the early years determines the mind. It is the hardware that has been hardwired. Some experts said after the child has developed reasoning power, anything he thinks will base on such language. If he then learns a second language, it will be developed on top of the first, with a fast translation going on all the time.
This is the scientific foundation of MOI. When a Chinese student learns science in English, he will automatically translate the English words to Chinese before reasoning. When there is no Chinese word equivalent, the mind will stuck for a while. I always have this problem working in different languages. The mind slows down when I come across a proper noun, or when I am doing mathematics. On fast reading, I am still confused sometimes with the meaning of 100,000 or 100 million in Chinese. I changed to English MOI in secondary school. I recall that I could not understand very simple arithmetic questions set in English. It took me one to two years of dreaming before I caught up, but still in the process of studying in English and thinking in Chinese. If I was taught in Chinese, I could be much better and could become DGG before I retire. It is a miracle that I am now thinking in Chinese and writing in English, still slow after so many years of hard practice.
When I was in EMB, I came across discussions on MOI. It seems nobody considered the scientific factor seriously. The whole thing was turned upside down for political reasons. First, English is important as the world uses it. I wonder how true this statement is. But with USA dominating the world and the British colonial background of Hong Kong, no one asks why the Chinese study in Chinese, French study in French and Spanish study in Spanish, etc. It is true that a lot of people study English as the official and commercial language in Hong Kong. But it is like looking at the sky from the bottom of a well. Chinese has no problem in UN, but English has problem in South America. Another factor comes from parents who need their children to be taught in English, probably not for the good of the children but for the parents. Schools conform to market force. Legislators cry out on the wrong education policies, whatever they are. The bottom line: not enough teachers to teach English. When there are, they failed the Language Proficiency Assessment. I think we need to teach and test mind-crunching subjects in mother tongue, while concentrating on teaching English as a second language.