Primaries are being given the chance this term to use national tests specifically designed for their brightest pupils for the first time in nearly a decade.
The optional tests in the three Rs will show whether children have achieved national curriculum level 6 - two levels above the expected for pupils in their final primary year.
The Government has ruled out using the tests, last used in 2002, as accountability measures in league tables or floor targets for "this year". But it says they can "help inform schools' statutory teacher assessment if they wish". Some educationalists believe the tests could quickly become "high stakes" in some schools - encouraging more teaching to the test - even if they do remain optional.
They are being introduced despite concerns from the National Foundation for Educational Research (NFER) that it may not be appropriate to award level 6 to primary pupils who have not studied elements that the level 6 curriculum introduces in secondary schools.
Several other unnamed respondents to the ongoing Government-commissioned Bew review into key stage 2 testing have made the same point. The NFER has suggested a "high 5" as an alternative.
But a Department for Education spokesman said: "Ministers are clear they want the brightest kids stretched - so they didn't see a reason not to make the tests available on an optional basis."
If the level 6 tests were used as accountability measures they could help schools show that their brightest pupils had made above-average progress for the Government's new floor progress targets.
At the moment that is impossible for a pupil who achieves level 3 at the end of KS1 because an average two levels of progress is made between key stages - thus making level 6 the only way such pupils can show better than expected progress at the end of KS2.
John Bangs, a senior research associate at Cambridge University, said he was concerned that even optional tests could quickly become part of "high stakes" accountability in schools.
"Optional can become compulsory when heads are looking for chances to have simple pieces of information about their staff and about what an outstanding school they are," he said.
"If they are going to be made available on an optional basis, then teachers should play a central part in constructing them."
Russell Hobby, general secretary of heads' union the NAHT, said: "This doesn't do any harm but is potentially a distraction from the main work of getting pupils up to level 4 and 5. But to have these resources available for more able pupils isn't a bad thing."
The DfE spokesman said: "We're making the test available for schools to use with high-achieving pupils. It's entirely down to them whether or not they use them.
"Lord Bew is looking in detail at how the assessment system can best stretch the brightest children."