The operation of what is known as the asymmetric week will be discontinued despite opposition from some heads, teaching unions and the Liberal Democrats. But Tory councillors backed the Labour administration's move.
Friday closures, which will continue in primaries and secondaries, are intended to allow staff development time free from pupil contact and are unique in Scotland. A review last year, prompted by claims that many pupils also took Friday mornings off, decided to stick with the status quo.
Nursery staff are unhappy that they have been singled out. Schools say they will lose the extra time devoted to curricular preparation and in-service work. They are also concerned about inconveniencing parents who may have to collect older and younger children at different times of the day.
Security could be another problem if the nursery children are the only occupants of a primary school, heads have warned. The education department has undertaken to have separate door entry systems where needed.
But Mrs Maginnis made clear that it was the need to fend off competition from more flexible pre-five provision in the private sector which made a change in the nursery week essential. There were no plans to revert to the normal five-day week in primaries or secondaries, she said, although primary heads will be asked to account for how their schools spend Friday afternoons.
Edinburgh has commissioned research involving 750 parents who were about to place a child in pre-school provision. The study found that three-quarters were put off by the asymmetric system.
More than one in five pre-school children in Edinburgh opt for the private sector. Last year, the authority had to cut back on the number of nursery places as parents of 550 four-year-olds elected not to use council provision under the nursery voucher scheme.
Mrs Maginnis pointed out that the areas which suffered worst from cuts were among the most deprived in the city. "The choices made by higher income parents who can afford it and are willing to pay for private sector education have a direct bearing on those with lower incomes," she said. "We have to make our provision as attractive to parents as possible."
John Dobie, Edinburgh's acting director of education, acknowledged the reservations of nursery heads but said: "Their job and mine is to serve the public and I have occasionally to remind our headteachers of that."
Councils have been urged to enter partnerships with the private and voluntary sectors so that ministers' pledge of a pre-school place for every four-year-old can be honoured. But Edinburgh, like many other councils, is determined to provide as many places as possible to the growing irritation and alarm of the private nurseries. Last week the city's education committee agreed to a subsidised scheme of "wraparound" care, providing an initial 80 places in six schools for parents who want extended hours.
Leader, page 16