16 May 1976
Pupils at Phefeni Secondary School started boycotting classes in protest against the use of Afrikaans as medium of instruction in certain subjects in schools. The unrest spread to Belle Higher Primary School, Thulasizwe Higher Primary School, and Emthonjeni Khula Ngolwazi Higher Primary School. These boycotts were daily occurrences until the ultimate breaking point on 16 June 1976, when the Soweto uprising took place that caused uproar in South Africa and abroad, where it became the most talked about South African event internationally since the Durban Strike of 1973.
Source:
South African History Online