The row over refused Sats appeals is spilling into meetings carried out this term to set targets for 2011.
Many headteachers now believe that school improvement partners should ignore their Sats results as they cannot be trusted, and instead turn to teacher assessment.
Heads must agree targets with their authority about how much progress pupils will make in English and maths between Years 2 and 6.
This year, there has been widespread anger about the outcome of appeals against the writing grades.
Many schools have had almost no changes made to papers, despite huge shortfalls against their usual scores and a wide difference between reading and writing outcomes.
Schools with much lower than expected results are unlikely to use them to set new targets. The National Association of Head Teachers' advice is that they argue their teacher assessments are more realistic.
This raises the possibility that parents and taxpayers could have one set of data to judge a school's performance while the school and its local authority have another - a situation that the testing and league table system was set up to eradicate.
Duncan Mills, acting head of learning and achievement for the Isle of Wight, said the authority was aware of nine of its 14 middle schools having returned scripts for review and that minimal changes had been made as a result.
He said: "Sips do have both sets of data. Their job will be to analyse the strength and weaknesses of the cohort that has just taken the test. The Sips will look closely at test outcomes to see if there is a mismatch between teacher assessment and test outcomes. They use both sets to arrive on a view of a school's performance."
The reason for such large drops is not clear: some blame the question; others say their marker was not up to scratch; others have said the mark scheme itself was poor.
Ian Foster, assistant secretary of the NAHT, said: "If the marks are wrong, for whatever reason. heads' careers are potentially at risk, through no fault of their own."
Adrian Hayes, head of Our Lady Immaculate RC Primary in Chelmsford, saw level 5 English scores drop from 50 per cent in 2008 to 15 per cent this year.
He said: "They won't say, `You got 15 per cent so your target is 20 per cent' - and I wouldn't go down that route because it would not be good for the school. But they can't have it both ways. Either they accept our teacher assessment, which they probably will do because it suits them to set higher targets, or if they use the test scores and say there are declining standards, then they can only set us a target that is not much higher than them."