New Labour's centralised control of schools has damaged primary education, according to research from the biggest inquiry of its kind for 40 years.
Government influence in the classroom has increased significantly since 1997 with the development of a "state theory of learning", academics found.
Children spend too much of their time preparing for "batteries of tests" in English and maths at the expense of a broader education in other important subjects, the research warned.
The result is that educational standards may actually have fallen in recent years.
The reports formed part of the Cambridge University-based Primary Review, a major ongoing inquiry into primary education in England.
One study, by Dominic Wyse, from Cambridge University, and Elaine McCreery and Harry Torrance at Manchester Metropolitan University, said: "Government control of the curriculum and its assessment strongly increased during the period from 1988 to 2007, especially after 1997.
"The evidence on the impact of the various initiatives on standards of pupil attainment is at best equivocal and at worst negative.
"While test scores have risen since the mid 1990s, this has been achieved at the expense of children's entitlement to a broad and balanced curriculum and by the diversion of considerable teaching time to test preparation."
There have been "some" improvements in standards achieved by many pupils in primary schools.
But the report also found "a decrease in the overall quality of primary education experienced by pupils because of the narrowing of the curriculum and the intensity of test preparation".
