Beechwood, a 580-pupil comprehensive in Slough, started sending pupils home for a day a week after beginning the term without a third of its teachers.
The local authority said the school - which normally has 38 staff - has 10 vacancies and two teachers on long-term sick leave, was unable to offer a "full curriculum in a safe environment".
Each year group is sent home on a different day of the week, and given work to do out of school.
Ron Austin, the headteacher, said the school had used seven supply agencies to try to find
temprary staff, but had only managed to recruit five. As a result full-time staff had to give up free periods to keep the school open.
He added: "If you are asking staff to work in their free periods, inevitably someone will go ill."
The school had advertised locally and nationally, without success. Mr Austin said that Beechwood was suffering from its position - it has recently been taken off special measures.
The situation is a striking example of the current recruitment shortfall. Meanwhile, new figures show that teacher-training institutions are turning away more male applicants than women - despite the shortage of male teachers.
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