As a dedicated educator, Mr Cheung knew that most Chinese students in Hong Kong, who are taught English as a subject in primary school and speak Cantonese at home, simply cannot cope with learning everything in English in secondary school.

For years, he argued that the policy of letting schools decide whether to teach in English or Chinese had failed Hong Kong miserably, and that the rush to send children to English grammar schools regardless of their competence in the language had led to problems in learning motivation, attitude and school discipline.

'Is it realistic and educationally pragmatic to expect the masses to benefit from an education done in a foreign language? I ask the people in high places in government, commerce, industry and education: Has it ever dawned on you that with the present policy, what is happening in school is hurting the education of the masses badly?' he once wrote in an article published in the Post.

Mr Cheung was a member of the Education Commission in 1990 when it laid out a timetable for the full-scale implementation of mother-tongue education by 1998. He was subsequently appointed vice-chairman of the Chinese Textbooks Committee, which was in charge of inducing publishers to produce sufficient textbooks in Chinese to meet future demands.

Unfortunately, his courageous move to change Carmel's teaching language proved suicidal, for the school and himself. The notion that one must use English to learn every subject to achieve fluency in the language was so entrenched that parents shunned Carmel after it became a Chinese-medium school.

Three years after adopting Chinese as the teaching language, faced with a decline in the quality of its student intake, the staff demanded to switch back to teaching in English. The school council sided with the staff, leaving Mr Cheung with no choice but to resign from the school he helped found in 1964.

Afterwards, he became principal of Pui Ching Middle School, an established Chinese-medium school. In 1991, Mr Cheung left Hong Kong for London, where he became a minister with the Chinese Overseas Christian Mission.

Now retired in the US, Mr Cheung still keeps abreast of developments in Hong Kong. In a recent letter to the Permanent Secretary for Education and Manpower, Fanny Law Fan Chiu-fun, he criticised how the mother-tongue policy is being implemented.

To him, requiring most schools to teach in Chinese but allowing about 100 to teach in English is worse than the previous practice of allowing schools to choose their own teaching language. Chinese-medium schools are still stigmatised as inferior.

'If government allows such a situation to go on, it is unethical,' he says.