The process standardizing Swahili was begun by the British administration well before independence. 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. Its codification involved developing a standard spelling system, describing the grammar of the variety selected as the new standard, and writing a dictionary to record its vocabulary.
Following Tanzanian independence in 1961, Swahili was used in more and more contexts for education, administration, politics and law. Its vocabulary was expanded to meet the demands of new contexts borrowing freely from Arabic and English as appropriate. President Nyerere intended that eventually it should be used for post-primary education, in the Higher Courts and in all areas of government. This meant intensive work in order to develop the necessary vocabulary and technical terms, and an enormous amount was achieved in a short space of time. In 1984, however, the government decided not to extend Swahili-medium education to secondary and tertiary education. English has been retained for these levels.