Research by The TES this week found some schools are dropping out of the pilots because of the extra work they pose for teachers.
The tests are a key part of the Making Good Progress scheme (see box, below), a central element of the 10-year Children's Plan, unveiled by ministers this week. Separate tests are being created for reading, writing and maths at levels 3-6 for both KS2 and 3.
Rather than sitting a single test at the end of a key stage then discovering their level, pupils will sit tests for each level when their teachers think they are ready. There will be two opportunities a year - in December and June - to take the tests.
Last week, hundreds of selected KS2 and 3 pupils in 10 local authorities took the 50-minute tests. They will still sit the standard Sats in May. But if they do better in the pilot, the higher level will count, both for the school's internal monitoring and league tables.
Under the second element of the trial, selected pupils believed to be at risk of falling behind in either English or maths are being given individual catch-up tuition.
So how did the first round of tests go? The TES spoke to 18 of the 484 schools originally listed as taking part and found they had diverse opinions: most teachers liked at least some aspect of the new system but were concerned about others. Several schools said the tests were less stressful for pupils.
Janet Widdas, headteacher of Riverside Junior School in Hebden Bridge, West Yorkshire, said she had only entered a small sample of children, who had hardly been aware they were taking the tests until the day itself. Detailed coaching was impossible, she said, as the tests were entirely new.
She said that, if the teacher assessment was right, children would not be faced with many questions they could not do, as sometimes happened with Sats.
"A test when the teacher thinks the child is ready will be a big step forward," she said. Meanwhile, to alleviate some of the stress of the June tests, Barry Hawes, head of Prettygate Junior in Colchester, Essex, entered all 64 of his Year 6 pupils in last week's trial.
"The big thing for me is that we are moving away from all the pressure in Year 6," he said.
Peter Price, head of St Christopher's Catholic Primary in Speke in Liverpool, and chair of the National Primary Headteachers' Association, said he worried that in future teachers would feel the need to get pupils practising extensively, and that lessons might be dominated by test preparation.
Ms Widdas said teachers could avoid this and should resist the temptation to enter pupils for test repeatedly in the hope they perform above their true level.
The second aspect of the trial - individual tuition - has been welcomed by many schools. But there appear to be teething troubles. Ms Widdas said it had been very difficult to find tutors, particularly in maths. An advert in a local newsletter, which usually yielded volunteers, had been unsuccessful.
Cliffe Hill Community Primary in Halifax, West Yorkshire, said it would not be offering hour-long individual tuition. Instead, it will provide half-hour bursts to groups of four or five, so more pupils benefit.
But the biggest difficulty with the new test appears to have been workload. Of the 18 schools The TES approached, seven had not entered any pupils for the tests this term, and five of these had pulled out of the pilot entirely.
White Court Primary in Great Notley, Essex, is one that withdrew. Melanie Vine, the head, said: "We are a small school, we had had some staffing changes, and I felt we could not put as much into it as we wanted to. From the schools I've talked to, it's an awful lot of work."
Several schools said a lot of paperwork was needed to prepare the teacher assessment. Nola Van Dam, head of St Thomas More Catholic Primary in Bexley, south-east London, described the workload as "enormous". Her school would not have got involved had it known this, she said.
The tests were drawn up in two weeks, principally by Sue Hackman, the Government's standards adviser, before the pilot was announced in January. There was little input from exam experts outside the Government or Qualifications and Curriculum Authority.
One said: "It has been much too short a development process. It is very difficult to develop a brand new testing instrument to political timescales."
A fuller picture of how the tests have fared will only be possible when the first results are released to schools on January 18.
WHAT IS MAKING GOOD PROGRESS?
- It is a trial, looking at alternatives to the present national tests for pupils in key stages 2 and 3.
It has four elements:
1. Testing children when their teacher thinks they are ready.
2. Individual tuition for pupils struggling with English or maths.
3. Progression targets measuring the proportion of children making two levels' progress during a key stage.
4. Cash incentives for schools that do well.
It began in September, originally to run for two years. Last month, it was extended to 2011.