Stop revising science, Year 6 teachers have been told, as the first science sample tests for more than 20 years are prepared to run this summer.
Primary schools will be told in the next few weeks whether they will take part in the first round of sample science tests for 11-year-olds.
About 775 schools, covering 5 per cent of Year 6 pupils, are due to administer the science papers on May 14 this year.
Schools taking part in the sample tests will get the results back at a school and national level, but this feedback will not be provided to either Ofsted or to local authorities.
The test scripts - which will not be returned to schools - will be used to monitor national standards.
A spokeswoman for the Qualifications and Curriculum Development Agency said: "Whether selected or not, schools should carry out their existing plans for the teaching and learning of science. The purpose of sampling is to obtain an insight into national standards - selected schools should not do any additional preparation with pupils for the tests."
One teacher, who wished to remain anonymous, said her headteacher had agreed to scrap intensive science revision for the first time. "I know that if we are chosen to do the sample tests in the test week, our results would plummet," she said.
But David Fann, chair of teaching union the NAHT's primary committee, said: "They (schools) don't trust the Government. If you are part of that sample, then they will revise."