Baseline tests for reception pupils in England are not reliable enough to measure progress this year, says a study for the Department for Education.
The education department, which is introducing the tests, says it would be "unfair" to use them as a measure.
There are three different testing systems that schools can use - but the study says the results are not "sufficiently comparable".
A head teachers' union said: "It is hard to avoid saying 'we told you so'."
Tests for pupils at the beginning of school, known as "baseline tests", were intended as a starting point against which to measure progress through primary school.
But they have faced opposition from teachers' union leaders who criticised them as introducing an unnecessary set of tests for young children who had just started school.
The Department for Education has now backed away from using the tests for measuring progress this year - after publishing a study that it had commissioned looking at the comparability of the three testing systems.
"That study has shown that the assessments are not sufficiently comparable to provide a fair starting point from which to measure pupil progress," says a statement from the Department for Education.
"In light of that, we will not be using this year's results as the baseline for progress measures. This would be inappropriate and unfair to schools."
The study from the Standards and Testing Agency concluded that the tests in literacy and numeracy, with three separate systems in use, were not sufficiently comparable.
Schools could choose between versions of the test provided by Early Excellence, Durham University's Centre for Evaluation and Monitoring (CEM) and the National Foundation for Educational Research (NFER).