They fear plans to launch a single system of assessments for children as they start school will create new league tables and be used to judge which teachers receive salary bonuses.
"There is serious danger of assessments for young children being corrupted from on high," said Professor Peter Tymms at the University of Durham. "What was a simple, localised system of helping teachers identify children's needs is now coming under increasing pressure to become part of a national system for judging schools and teachers."
Baseline testing was introduced last September as a means of assessing a child's ability on starting school. A total of 600,000 children were tested in reading, speaking, listening and concentration within their first seven weeks.
Ministers say the tests help teachers to plan each child's education and identify potential problems. However, with more than 90 accredited schemes, there is currently no way of comparing data nationally. Schools are expected to discuss assessments with parents, who have the right to request their child's results. LEAs can also compare data locally.
David Hawker, of the Qualifications and Curriculum Authority, said ministers are looking to introduce a single system within the next two years.
"The feedback we've received from our evaluation of baseline testing is clear cut - teachers want a common system. It would also make sense to parents. It's up to ministers if they choose to publish that information." The current schemes are accredited until 2000.
Professor Geoff Lindsay of Warwick University's Institute of Education has criticised some of the schemes used, but does not want to see a national system.
He said: "There's only one reason ministers want to see one and that's to judge schools."