In the 1855, reports from school inspectors in the various colonies later become states reported mispronunciation of vowels and diphthongs by the younger students. A diphthong is a sound formed by the combination of two vowels in a single syllable, where the sound begins as one vowel and moves towards another (as in coin, loud, and side). There are diphthongs in every English accent, but they are very pronounced in the Australian accent.

Later in 1890s, it was suggested that elocution teachers taught a particular way of speaking became sought after for lessons in British vowels and diphthongs within the socially aspirational classes. This “sought-after” form of speech is said to have become what is now known as Cultivated Australian.

However, in 1893, The Chief Justice of Victoria, Sir John Madden, is recorded to have scolded young Australians for mispronouncing their diphthongs and then encouraging them to "pronounce the English vowels as they were intended."

In 1916, there's an initiative in schools to teach Australian the "correct" pronunciation of vowels and diphthongs that include lessons like correct lip and tongue placements.

The first general Australian dictionary was published with Graeme Johnston’s Australian Pocket Oxford Dictionary in 1976.

From 1980s and onwards, individuals with “Broad” and “Cultivated” accents are dwindling, and the majority of Australians are adopting the “General” accent instead.

Meredith Eriksson. (2018, September 12). How Australian English Grew Its Wings. https://www.babbel.com/en/magazine/history-of-australian-english