Ministers have refused to make public the findings of a crucial review into their controversial multi-billion-pound academy programme.
The review, by the Prime Minister's delivery unit, was announced in November and has been used by ministers to accelerate plans to create more than 400 of the privately sponsored state schools.
The TES made two requests under the Freedom of Information Act for the release of the report, which was completed in January.
The Department for Children, Schools and Families (DCSF) and the Treasury both accepted that the public interest would be served by disclosure of the review's findings but said this was outweighed by ministers' need to be able to receive candid, confidential policy advice.
Ministers told Parliament in November that the review would examine whether academies were "meeting the objectives of turning around attainment in underperforming schools and ... addressing a culture ofunderachievement and low aspirations in some of the most disadvantaged communities".
Ed Balls, the Children, Schools and Families Secretary, said: "Because of the scale of the resources that we are spending on this programme, it is right to ensure we deliver value for money."
Reports have suggested the delivery unit study found variations in standards between academies and differences in their level of collaboration with local authorities.
John Bangs, head of education at the National Union of Teachers, said it was "absolutely essential" the report was published. "It is in the public interest to know exactly what contribution the academy scheme makes to the efficient delivery of education," he said.
Lord Adonis, the schools minister, said in January that the only change to the academies scheme would be its acceleration.