Mark my words
Chinese-language chauvinists take note: Cantonese is anything but a minor southern dialect of only localised importance.
A distinct, rich language, with numerous regional variants, Cantonese is spoken as a mother tongue by 64 million people in Guangxi and Guangdong (including Hong Kong and Macau), and several million others worldwide, mostly in Southeast Asia but with significant numbers in North America and Australasia.
From the mid-19th century, government vernacular schools in Hong Kong used standard Cantonese as the teaching medium. Most children had to work from an early age and compulsory primary education was only introduced in the early 1970s. In what were, until recently, rural districts, such as Hakka-populated Tsuen Wan, few inhabitants spoke much Cantonese anyway and only learned it at school.
While better than nothing, vernacular education was not seen as a route to advancement. All but the most menial government posts, and commercial life, required some English. For this reason, most Hong Kong Chinese parents have sent their children to English-medium schools whenever possible.
One reason advanced for China's weakness in the face of 19th-century foreign aggression was that its people couldn't all speak the same language. Dr Hu Shih and other prominent reformers led the drive for the popularisation of the Peking dialect, which became known in English as Mandarin, from the administrative elite who were almost the only people who spoke it. In a move towards linguistic democratisation, Mandarin became known as kuo yu ('national language').
The teaching of Kuo yu was an outgrowth of the May Fourth Movement, an outpouring of intellectual nationalism that started in 1919. The term Putonghua ('common speech') was only invented after the communists came to power, and has gradually become Anglicised as a politically correct term for the same language.
Schools opened in the 1920s, such as Munsang College in Kowloon City, taught exclusively in Mandarin. Educational standards were generally high. In addition, inculcating race-based Chinese nationalism among overseas populations, especially in Malaya and the Straits Settlements, was an inherent part of the curriculum. Other well-known Mandarin-medium schools include Pui Ching Middle School, Kiangsu and Chekiang College, Fukien College, Heung To Middle School and Pui Kiu Middle School. Most retain a 'patriotic' - in practice leftist - focus.
Putonghua-medium schools became widespread in the early 1950s, when large numbers of emigre Chinese from cities further north moved to Hong Kong. These newcomers didn't understand Cantonese and usually viewed the language, and those who spoke it, as less than civilised. Wherever possible the new immigrants put their children through Putonghua- or English-medium schools. Most expected to eventually return to the mainland when circumstances permitted, and proficiency in kuo yu, not a regional language, was what mattered.
A student population increasingly politicised by language policy was recognised as a threat to social stability by the 20s. Sharply conflicting notions of what constituted 'patriotism' contributed to the Nationalist-inspired riots in 1956 and the Communist-fomented ones in 1966 and 1967. After the Chinese civil war, Nationalist- and Communist-funded schools in Hong Kong competed for students, each extolling radically differing versions of both the recent past and the future role of the 'glorious motherland'.
Between the end of the civil war and the late 50s, more than two million people decamped to Hong Kong from the mainland specifically to escape social chaos, and wanted no part of anything that looked like creating more of it. Heated local debates over 'patriotic' or 'national' education still erupt every now and then.
Millions of overseas Chinese understand Cantonese due to the popularity of Hong Kong films, music and television programmes.