Hundreds of thousands of secondary school pupils in England are set to finish the school year without receiving their Sats results.
The latest figures for the delayed tests taken by 14-year-olds show that 29% of English results, due by 8 July, are still not ready for publication.
Shadow Schools Secretary Michael Gove is calling for an interim report next week from inquiry head Lord Sutherland.
Head teachers have warned of record levels of appeals over marking.
This year's Sats test results for primary and secondary pupils have become embroiled in missed deadlines, lost papers and allegations over the quality of marking.
The reports of delays with the secondary results has prompted the Conservatives to call for an immediate report from the independent inquiry, claiming that "confidence in the government's handling of our exam system is collapsing".
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Yesterday Mick Brookes, the General Secretary of the Association of Head Teachers, said: "I have had a steady flow of emails from colleagues reporting problems. One person is saying that half of his English Sats are marked wrongly, mostly in the adding up of the scores. Scores are being calculated incorrectly.My suggestion to Prime Minister Gordon Brown: Cancel the ETS contract, and return to the traditional British system of examinations...
"I have also heard from a head in Cornwall, who says that his papers are at a school in Kent, because ETS has not managed to pick them up."