The devil of moving from opposition into (probable) government is that you have to work out how to implement your pledges.
Tony Blair, the Labour leader, has been careful to make only five "early pledges". But one that parents and teachers will be watching is to reduce class sizes for five, six and seven-year-olds to a maximum of 30 within the lifetime of a first Labour government. That means action on an estimated 15,000 infant classes in England alone.
So far, attention has focused on the pledge's other half: phasing out the Assisted Places Scheme, which will pay for reduced infant class sizes. The Government and the independent schools have rushed to point out that savings from one will be too little to pay for the second.
The National Foundation for Educational Research, extrapolating from a local pilot study, has put the figure at only an extra #163;60m a year for an extra 2,300 teachers, the amount that should be released from the Assisted Places Scheme in 1999-2000.
Rather than using the stick of legislation to restrict class sizes to 30, Labour plans to use the carrot of specific grants. LEAs would be invited to bid for money in exchange for producing convincing plans to reduce all their infant classes to 30 or below.
But, as more than one local authority has pointed out, this would simply enable the LEA to give schools sufficient funds to reduce class sizes; under local management, the authority would have no power to compel them to use it for that purpose.
David Whitbread, education officer of the Association of County Councils, believes schools should keep that flexibility to organise their classes as they think best. "If you start making things absolute, you start running up against the local discretion of the school," he said. "But if you said no school budget should make it necessary to have more than 30 in an infant class, we could live with that."
In fact, Labour plans to back up the funding with guidelines to LEAs on working with schools and advice to parents about the effects on intake of smaller classes. For the effect would undoubtedly be to restrict the intake to popular schools in some cases - although, in others, extra classrooms would be added. In small schools, there would be more mixed-age classes. Choice would be further curbed by new Labour guidelines on admissions which would oblige appeals committees to take account of the new policy on class size.
LEAs have been quick to point out factors against a rigid ceiling on infant class size, however: the physical size of a school might make it impossible to add classrooms.
Some authorities have already succeeded in virtually eliminating large infant classes. In the inner London borough of Newham, for instance, the authority has been funding primary schools for five years so that none need have classes over 30, and governing bodies and unions have pledged to try to stick to that figure.
Where a class does slip over 30, either the school or a teaching union can call for a special "monitoring panel" to be convened.
This panel, consisting of teacher and governor representatives, is chaired by Graham Lane, who chairs the borough's education committee as well as the association representing metropolitan LEAs. It tries to find out if every alternative to an oversized class has been explored and if some temporary measure could help.
"The panel has only been called four or five times in the last five years and a solution has never not been found," Mr Lane told The TES. This year, to avoid problems caused by rising rolls, the borough is putting in extra money to help schools keep reception classes to 25.
Emboldened by his experience in Newham and by Labour's pledge, Mr Lane summoned Labour chairs of education at the start of the year to ask them to start working on plans to reduce infant class sizes. The plans will be discussed at the first conference of the newly created Local Government Association in June.
But, as one local government spokesman said: "Newham is not as bedevilled by parental demand as some LEAs are." Moreover, its spending is generous.
While some authorities have few or no oversized classes, others - including the London boroughs of Kingston and Redbridge, Trafford and Tameside in Greater Manchester, and Staffordshire, have a great many. In Staffordshire, for instance, no fewer than 228 primaries have at least one infant class with more than 30 pupils.
Labour is cautious about the speed of implementing its pledge. "We fully expect this to be achieved within our first parliament, " said a spokeswoman for David Blunkett, education spokesman. "But there's no formal timescale because of varying circumstances. We're going to be pragmatic."
But the existence of the pledge will produce its own momentum. Pressure from parents and teachers may do more than any government exhortation to bring down large classes.