Ministers and their advisers meddle in the detailed workings of England's assessment system despite lacking the necessary expertise, researchers have claimed this week.
The report, from the Assessment Reform Group, also argues that exam and test results should be published with "health warnings" setting out the likelihood of error and explaining what raw figures really say about a school's performance.
The academics estimate that more than pound;750 million a year is being spent on an assessment system that is supposedly controlled by experts from Ofqual and the Qualifications and Curriculum Development Agency.
But the report says remit letters mean that "in practice, ministers have exercised extensive powers".
It adds: "While no one would contest the right of elected politicians to determine overall assessment policy, their involvement in specifying technical details of assessment models and procedures raises questions over whether they, and some of their advisers, are sufficiently qualified to do so.
The academics cite single-level tests where they say all the basic characteristics were set out by the Government rather than assessment experts, leading to tests that are "of questionable legitimacy from a technical perspective".
The report also says policy makers should question whether they are trying to put assessment data to too many different uses and whether it is up to the task.
"Conventional school examination data should be published with this `health warning': that they measure only part of a school's business and that these results are influenced by factors beyond the school's control, such as the prior attainment and background characteristics of its pupil population," it says.
"Consideration should be given, also, to acknowledging the existence of error in the marking of tests and examinations."
The paper argues that the Government's pound;150m Assessment for Learning (AfL) policy shares little of the spirit of the original concept, designed to help teachers and pupils work out how much has been learned and what they should do next.
It says true AfL practice has been patchy because of the "performance culture" in schools which puts teachers under pressure to raise published test and exam results.