Mandarin (the standard language of China based on northern dialects) has been used as a lingua franca in Singapore alongside Hokkien (a south-eastern Chinese topolect) since the end of the Second World War.
Before the standardisation of Singaporean Mandarin in the year 1979, Mandarin was largely used in a colloquial form based on the speech of Beijing, with infusions from various southern non-Mandarin Chinese varieties such as Hokkien, Teochew, Cantonese, Hainanese and Hakka.
This colloquial form of Mandarin served as a bridge between speakers of various mutually unintelligible southern varieties.
Mandarin was also the language of instruction in the now defunct Chinese-medium schools and education system.
The use of Mandarin in the Chinese-medium schools led its use mainly by the Chinese-educated or Chinese elites in Singapore.
Some could speak other Non-Mandarin Chinese varieties or English most of the time and have less exposure to Standard Mandarin.