Sir Alexander Mackenzie Senior Public School

The Toronto District School Board (TDSB), formerly known as English-language Public District School Board No. 12 prior to 1999, is the English-language public-secular school board for Toronto, Ontario, Canada. The minority public-secular francophone (Conseil scolaire Viamonde), public-separate anglophone (Toronto Catholic District School Board), and public-separate francophone (Conseil scolaire catholique MonAvenir) communities of Toronto also have their own publicly funded school boards and schools that operate in the same area, but which are independent of the TDSB. Its headquarters are in the district of North York.

The TDSB was founded on January 20, 1953, as the Metropolitan Toronto School Board (MTSB) as a "super-ordinate umbrella board" to coordinate activities and to apportion tax revenues equitably across the six anglophone and later a francophone school boards within Metro Toronto. The MTSB was reorganized and replaced on January 1, 1998, when the six anglophone metro school boards and MTSB merged to form the Toronto District School Board. The francophone school board of MTSB was amalgamated with several other Francophone school boards in the region to form Conseil scolaire Viamonde.

Today, the TDSB is Canada's largest school board and the fourth largest school board in North America.