"None of the providers we have interviewed thought the vouchers had brought parents to their establishment who would not be coming anyway," Gillian Pugh, director of the NCB's early childhood unit, told a conference in London on Tuesday.
"Some parents in all four authorities have described being pressurised by schools to send their children to reception classes in September if they wish to be sure of a place, sometimes earlier, and for more hours than parents themselves would wish."
Mrs Pugh was presenting interim findings of her independent evaluation of the voucher pilot in Norfolk and the London boroughs of Wandsworth, Westminster and Kensington and Chelsea to a conference at the University of London's Institute of Education.
She said 60 per cent of parents surveyed had chosen where their four-year-olds would go by the time of the child's second birthday.
Other main concerns highlighted in her report are that the voucher is not covering the costs of setting up or expanding groups and that the "heavy burden of administration" will always be time-consuming, particularly for headteachers and heads of nurseries and pre-schools.
The term "nursery vouchers" is misleading, said Mrs Pugh. "This is an initiative that at present is more about four-year-olds starting school early than about nursery education." The gradual move to take children into school earlier is "one of the most unfortunate consequences of the voucher scheme", she said, "although it is still far from clear how many schools have changed their admissions policies".
Although there has been nursery expansion in Norfolk, there has also been some contraction in the playgroup sector, as well as concerns among private providers about their viability (see story opposite).
There is little evidence so far about the scheme's impact on quality, said Mrs Pugh. However, all four pilot LEAs felt that the Government's targets for four-year-olds "expected a rather lower level of performance than the LEA would expect of its own provision".
The "Desirable Outcomes for Children's Learning", which sets targets of achievement for children at the end of pre-school, "were not sufficiently advanced to meet the educational capabilities of four-year-olds".
Meanwhile, a report from the Pre-school Learning Alliance notes that staff in all the pilot areas needed additional training to help them deliver the required learning outcomes. However, Mrs Pugh said, "there is no evidence yet that voucher income is sufficient to support that training".
There is much concern about the quality of education received by young four-year-olds in reception classes, where there may be one teacher for 35 children and where the education may be too formal for them. "We feel that this is one of the most serious problems facing the education system at the moment; it is not a consequence of the voucher scheme but has been exacerbated and highlighted by the scheme."
Schools Minister Robin Squire told the conference that "the success of the scheme in the Phase One pilot areas is undeniable". He pointed to high take-up figures, the creation of 800 new nursery places in Norfolk and evidence that 40 per cent of nursery providers expect to expand over time.
Myths that the scheme would be a "bureaucratic nightmare" were unfounded, he said. Mr Squire pointed out that 72 per cent of parents and 60 per cent of providers found the paperwork easy or very easy. He said the scheme was now fully prepared to go national next April.
However, headteachers in Wandsworth this week called for the scheme to be abandoned. They said that it neither offered value for money nor improved the quality of education.
Joan O'Pray, primary representative on Wandsworth Standing Conference of Headteachers and Principals, and head of Sheringdale Primary, said: "The rest of the country is being forced into this because we have done the job well and proved that we can collect vouchers. No one has done any analysis of whether there are any educational benefits and this makes me extremely angry and sad."