In the 1920s, a southern variety of Swahili, used in Zanzibar, was selected as the basis for the standard. The fact that it was being used in primary education and for administration meant standardization was essential. And developing a standard spelling system, describing the grammar of the variety selected as the new standard, and writing a dictionary to record its vocabulary.
In 1984 Swahili was used in more and more contexts for education, administration, politics and law.President Nyerere intended that eventually it should be used for post-primary education, in the Higher Courts and in all areas of government. However,the government decided not to extend Swahili-medium education to secondary and tertiary education. English has been retained for these levels.