By Gary Eason
Education correspondent, BBC News
School exchange trips will not be covered
What should be the test of whether someone needs to be vetted for their suitability to work with children?
Should it be the frequency of contact they have and the likelihood of their posing a risk?
Or should it be the prevailing climate, in terms of political response to the public perception of risk?
The chair of the new Independent Safeguarding Authority, Sir Roger Singleton, has been explaining why the rules are being changed even before they have taken effect.
The issue of checking people working with children has had a chequered recent history that is worth remembering.
In March 2002, the Criminal Records Bureau (CRB) had taken over the administration of the checking system.
This was supposed to pull together the existing system of separate checks on the government's lists of barred people, and on police criminal and intelligence records.
Within two months this had reached such a crisis that the government had to revert to the old separate system.
Classroom staff could start work, provided they were not on a banned list, pending completion of their police checks.
August brought a second U-turn. Following the murders of Jessica Chapman and Holly Wells by a school caretaker in Soham, Cambridgeshire, the Department for Education told local authorities that those interim arrangements must cease to apply from the start of the autumn term.
In response to public alarm it said it was crucial that the full CRB checks should be completed before someone started working with children.
Chaos: as the autumn term began, schools had to turn away pupils or close altogether in some cases because they did not have enough staff who had been vetted to put in front of classes.
Education Secretary Estelle Morris reverted to the old system and gave head teachers discretion to let people start work after checks on the barring lists, with a full CRB disclosure to follow later.
So a "crucial" requirement was swept aside by expediency.
The Bichard inquiry that followed the Soham murders found "very serious failings" in the police and vetting system.
Its recommendations led to the system that is now finally being implemented across England, Wales and Northern Ireland - and amended before it even starts.
Because since 2006 all has been quiet - or rather, the noise has gone elsewhere, diverted by the abuse of Baby Peter and the shortcomings identified in some children's services departments.
Baby Peter was killed in his own home, but the Singleton report specifically says private arrangements within families and between friends should not be covered by the vetting and barring system.
But Singleton's review of the vetting proposals grew out of the high-profile protests about the new vetting system, not the death of Baby Peter.
"In the summer of 2009, several children's authors raised concerns that the new scheme would require them to register because they regularly go to schools to give talks," he reports.
"They argued that they did not pose a risk of harm largely on the grounds that they did not have the opportunity to develop relationships with children because they worked in different schools on one-off visits."
Sir Roger told the Today programme on BBC Radio 4: "The scheme was developed really three years ago when the [Safeguarding Vulnerable Groups] Act went through Parliament in a rather different climate to the one that we have today.
"Then, if you look at Hansard, Parliamentarians were very keen to close down every possible loophole," he said.
"The atmosphere now is different. It's one looking for more balance and proportionality."
Sir Roger says he has proceeded on the basis of two general principles.
"The first is that in circumstances where parents exercise their own judgement about who should care for their children by making sensible and responsible arrangements between themselves, that is entirely a private matter in which the state should not interfere."
However where they give that choice to a school, club or other group - and cease to be able to make a personal decision about the carers - then registration is required.
But how are "balance and proportionality" applied to deciding who should be registered?
For instance, a school governor will have to be vetted - even though meetings are likely to be after school and events like an assembly will involve hundreds of other people.
But the same governor, as a parent, can have their children's friends in their home for a sleepover, without any regulation.
Where is the bigger risk?
Anyone can still set up as a private tutor and invite children into their home on a one-to-one basis, without any regulation.
Most glaring of all: as with the existing CRB checks there is no effective way under the new scheme to check the backgrounds of people from overseas, be they teachers - or volunteers.