Timothy Mortimer (Deputy) Sefton High School is a government-funded co-educational dual modality partially academically selective and comprehensive secondary day school, located in Sefton, a suburb in western Sydney, New South Wales, Australia.

Established in 1961, the school caters for approximately 1,100, students from Year 7 to Year 12 and is operated by the New South Wales Department of Education.

The students are a mixture of local students and academically selected students.

[1] Sefton High School received its first students on 30 January 1961, and became academically selective in 1989.

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