A total of 772 Welsh primaries have registered with curriculum body ACCAC to have the tests externally marked. More schools are expected to administer and mark the tests internally.
A Department for Education and Skills spokeswoman said the statistics supported its view on the importance of testing.
But Simon Gibbons, from the National Association for the Teaching of English, said he did not think the Welsh schools' decision undermined the case against the tests. "Schools use them because there isn't an agreed alternative and they are under the impression that parents think Sats are a measure of a school's achievement," he said. Welsh teachers say there is less test pressure, as results are not compiled into league tables.
Test papers were sent to all schools, but the decision on whether to use them was left to headteachers.
Kerry Waters, head of Ringland juniors, Newport, Gwent, said: "We find the tests useful for teacher assessments. They are going to be marked for free.
We would be silly not to use them."
Chris Jackson, head of Glasllwch primary, Newport, said: "There comes a point when children need to sit a test."
But Susan Eriksson, head of Trellech primary, Monmouth, will give children age-standardised tests from the National Foundation for Educational Research next month. She said: "We didn't have the hectic build-up (of previous years) . There are no children crying, having anxiety attacks or stomach aches."
The Year 6 tests were made optional in Wales this year following a review of assessment by Professor Richard Daugherty, of the University of Wales, Aberystwyth.
A moderation system for teacher assessment is now being developed alongside Year 5 skills tests. Next year, Year 6 papers will be available without external marking. Key stage testing is due to end entirely in 2008.
The Welsh Assembly said it consulted schools on the 2005 tests and found four out of five wanted optional rather than compulsory tests.