The chief inspector of schools has come out against "teaching to the test" this week in Ofsted's strongest statement on the subject to date.
Christine Gilbert said the phenomenon was becoming increasingly widespread, with both primary and secondary school teachers focusing on exam-passing techniques rather than developing pupils' wider skills and knowledge.
Her comments came in response to a highly critical report on national tests, written by the Commons' children, schools and families select committee.
The report, released in May, called for a radical review of national tests, describing teaching to the test as a "widespread" practice that left pupils unprepared for higher education and employment.
It also complained that tests were being used to make wider judgements about school performance.
Ms Gilbert's response to the report, published this week, agrees that the quality of education in some schools is suffering as a direct result of the testing system.
Some schools are able to prepare pupils for tests without sacrificing the wider curriculum, she says. But, referring to evidence gathered from inspections, an emphasis on the core subjects limits what pupils do, particularly as teachers prepare them for key stages 2 and 3 exams.
"Routine exercises and preparation for tests impair the development of understanding as well as enjoyment of maths, particularly but not exclusively at Year 9," she writes, adding that high-stakes testing is also having an impact on the range of teaching at GCSE and A-level.
Her comments will make uncomfortable reading for the Government, which denies that teaching to the test is common.
Barry Sheerman, the select committee chairman, confronted Ed Balls, Schools Secretary, with Ms Gilbert's letter last week, accusing him of not accepting evidence they had presented "time and time again" about teaching to the test.
But Mr Balls said: "It is not our view that teachers should be, or are generally, teaching to the test. But that is something we want to gather more information on."
He added: "Of course, part of learning is learning to produce information in an examination."
Mr Balls added that the Government's position was not "set in stone" and pointed to the introduction of single-level tests as evidence that they were open to change.
David Bell, permanent secretary at the Department for Children, Schools and Families, who appeared before the select committee, also refused to accept Ofsted's findings. In 2005, when he was chief inspector, he wrote in his annual report that too much time was being spent drilling pupils for tests.
Mick Brookes, general secretary of the National Association of Head Teachers, said: "If Ofsted are saying that the nature of testing is affecting children's education, when is this Government going to admit that the game is up?
"My colleagues are saying almost universally that the emphasis has to be put back on teaching, instead of this fixation with targets and tests."
Mr Brookes was not against pupils sitting the tests, but wanted them to be locally administered and marked, with the results used to help teacher assessment. Random sampling of results could then be used by ministers to make national progress checks, he said.
The committee's report said that test results were too often used to make judgements about overall school performance, which had a "distorting" impact on teaching.
But Ofsted's response denied that results were playing too large a role. Ms Gilbert said that inspectors also looked at pupil progress, contextual value-added data and the quality of teaching and leadership.
But her remarks came as Ofsted consults on proposals, including one to bar schools with low results from being rated above satisfactory.