The three-part lesson, used in primaries since the late 1990s to teach literacy and numeracy, can damage learning, influential advisers have warned.
Teachers should feel free to decide what works best and tailor their teaching to pupils' needs, rather than be restricted by government guidelines, according to the Advisory Committee on Mathematics Education (ACME).
The committee, part of the Royal Society, also said the "top-down" pressure on schools to improve test results has left some pupils feeling anxious about the subject.
The three-part lesson was a key component of the literacy and numeracy strategies, introduced in 1998 and 1999, with teachers encouraged to follow a standard plan for each 45 to 60-minute period.
In numeracy, the lessons are made up of a starter session of up to 10 minutes on oral work and mental calculation, followed by 40 minutes of main teaching activity, and up to 15 minutes of plenary time to sum up.
This structure has been seen as a contributor to improved key stage 2 test results. After its introduction, more than 90 per cent of schools are thought to have used it. Its effectiveness in literacy teaching has been criticised, but for numeracy it has so far been relatively uncontroversial.
Now, in a paper on the future of primary maths teaching, ACME said that many teachers followed the three-part lesson structure "without reflecting on its purpose or effects".
"Indeed, the impact of this structure on learning can be less than positive, even where schools believe they are doing an adequate job, eg where good key stage test scores are achieved," it said.
Margaret Brown, professor of mathematics education at King's college, London and an ACME member, said: "It's not that the three-part lesson in itself is wrong. It's that more variety would be useful."
Some tasks, for example, investigative work or revision, worked better spread out over a series of lessons, she said. In these cases, it was not helpful to have starters and plenaries.
Yet teachers often feared to depart from the standard format. In 2002, Ofsted was forced to warn inspectors not to insist on the three-part structure, following complaints that some had marked teachers down when their starter was "five minutes too long".
ACME also said that the pressure on schools over results had left many teachers feeling de-professionalised.
Tim Coulson, director of the national numeracy strategy, said this year's update of the strategy recommended that teachers did not always have to use the three-part lesson. He said: "We are not saying do not use it. But there needs to be a degree of flexibility, so that teachers choose the right lesson for the right day."