Nearly half of pupils taking national tests in English writing are awarded the wrong grade because of inaccurate marking, newly published research suggests.
Shockingly, the Qualifications and Curriculum Authority report containing the figures reveals the number of checks made to avoid such mistakes will be cut by two-thirds for this year's tests.
A QCA-commissioned study into key stage 3 marking indicates that in 2007 only 55 per cent of pupils taking the English writing test would have been awarded the level, or grade, deemed appropriate by a senior marker. In science it suggested 13 per cent of pupils received the wrong grade.
Kathleen Tattersall, chair of Ofqual, the exams watchdog, said: "The high level of misclassification in English suggests significant cause for concern."
Figures from checks on the marking of last year's tests suggest the situation was slightly better. But the QCA report admits that they will not be as reliable as the study undertaken in 2007 because the sample used will not be as representative.
Even so they will raise eyebrows, suggesting that a third of those taking KS3 English reading tests in 2008 were given the wrong grade and that only 64 per cent of those sitting the writing test got the correct one. For KS2 English, the checks suggested that 22 per cent of writing papers got the wrong grade and 13 per cent for reading.
There were other problems last summer with delayed results for 1.2 million pupils, and schools and markers left frustrated by disorganised training, multiple computer glitches, missing scripts and a failing helpline.
The rush to find a replacement for American contractors ETS will mean a move from an online marking checking system to a paper-based one this year. This will mean each marker's work will be checked twice instead of the six checks made last year.
Edexcel, which ran the tests in 2006 and 2007 and will replace ETS this year, claimed the QCA study was flawed and misleading and did not reflect the results actually given to schools in 2007 because it was conducted outside the marking period.
Last year a record number of schools queried their results, with more than 150,000 national test papers sent back for re-marking. Proportionately, the requests were particularly high in English, with almost six times as many primaries asking for reviews as in 2007.
Mick Brookes, National Association of Head Teachers general secretary, said the figures were "appalling".
"Teachers don't believe the marking is good," he said. "This is only the tip of the iceberg. Teachers don't tend to send back papers if they don't appear to cross a threshold boundary into another level."
But Ms Tattersall said: "The quality of marking in 2008 was at least as good as in previous years."
In a separate report Ofqual revealed that more than 22,000 A-level and GCSE grades were changed last year following queries from schools. They represented 18 per cent of the total queries submitted by schools on GCSEs and one in ten of those on A-levels.