It was last November that James McCullough got the summons. After 12 years running a successful school, his authority grabbed him to become No 2 in its special needs department. Seven months later, no successor has been found for his school. A new head is unlikely to start before January. Staff are blaming the National Professional Qualification for Headship (NPQH), which became mandatory on April 1, for a two-term interregnum that could threaten their stability and reputation.

The job was first advertised in February - a mixture of governor indecision and authority inefficiency explains the delay. The response looked promising: 11 people asked for application packs, four filled in the forms, two were shortlisted but withdrew on the day of interview. Two months later, another advert produced just one applicant. “There are a number of us who would have been quite willing to throw our hats into the ring when we saw the poor response,” says a senior member of staff at the school*.

“But the NPQH requirement rules us out now. We’ve been caught cold. A year ago there would have been no problem.”

The new regulations mean that, from April 1, prospective heads must have passed the qualification or be registered for it and complete it within four years. Few dispute how difficult it is to fill headteacher vacancies; the jury is out on whether this has made it even harder.

David Tuck, head of Dallow primary in Luton, is in no doubt. “I was at the NAHT conference (in Cardiff in May) and listened to John Howson, an expert in teacher supply, telling us that vacancies were heading towards the record of 3,068 set in 1997,” he says. “So reducing the field of applicants even further by insisting on an exam just doesn’t fit with the climate we’re in.”

Those heads with the NPQH are its fervent fans. Jan Atkins, head of Blue Gate infants’ in East London, is one. For her, it is quality not quantity that counts. “It is not enough to have more heads - they have to be good,” she says. “There are teachers being pushed to become heads who then find they are unable to complete the course. Not all deputies want to be heads.”

Since 1997, when the qualification started, it has been fully funded. Now schools will be charged 20 per cent of the total cost - paying out pound;725 for the two-year flexible course and pound;455 for the fast- track one. Small schools of 100 pupils or less will be exempt. But school are paying for training that will benefit another school if the candidate moves on.

There is a serious shortage of ethnic minority headship applicants. So how many are coming forward for training? The National College for School Leadership (NCSL) is unwilling to give numbers, saying its centres are working to augment the number of potential leaders from under-represented groups.

Lorna Jackson, originally from Jamaica and in her first headship at Maryland primary school in multiracial East London, agrees that more needs to be done to encourage people from ethnic minorities. She gained her NPQH as a deputy and sings its praises, but thinks that making it mandatory might put off aspiring heads.

Pauline Hoyle, Newham’s head of curriculum professional development, encouraged Ms Jackson to go for the qualification. She doesn’t see it as a block to filling vacancies but as a means of giving staff confidence to look realistically at whether they can be a head. “The course is more flexible now, but those who do it will not necessarily make good heads.

Other areas need taking into account. It should only be attempted once deputies have experience in the role.”

Jane Phillips, chair of the National Association of Governors and Managers, says governors know little about the course. “Primary school difficulties mean that people are being appointed who are not ready for the job. We don’t know if the NPQH will change this, but we do know that many primary teachers do not have time to get involved - and they might well be the sort of heads we need,” she says.

Terry Allcott of the Secondary Heads Association (SHA) says there is no evidence that the qualification interferes with the supply of heads. But SHA is not in favour of making it mandatory. “There are other ways that aspiring heads could plug the skills gaps rather than having to do what is set out for them.”

Richard Hart passed his NPQH on the day he was interviewed for the top job at the Thomas Aveling school in Medway - and is in favour of it being mandatory. “If people want to be heads, then the commitment to doing a professional exam should be part of it,” he says. “It’s important that professional development is sustained and award bearing.” But he says the profession is not doing itself a service by charging schools. “If we are serious about quality school leadership, then to effectively ration who takes an NPQH is a retrograde step.”

John Howson, of Education Data Surveys, says the NCSL needs to turn out at least 2,500 graduates a year to allow employers a decent field of applicants. Whitehall says it doesn’t see any evidence to suggest that making the NPQH mandatory will lead to unfilled vacancies. Its figures show that 3,300 graduated last year and 2,200 applications have been received for the current round.

But it’s not that simple. An NCSL sample of those who graduated between 2001 and 2003 shows that 40 per cent have gone on to headship and a further 4 per cent are acting heads. Of the remainder, the majority are seeking headships.

Critics of the qualification are concerned that such training means tomorrow’s heads could all be singing from the same hymn sheet. John Hill, head of Coleraine Park school, Haringey, who monitors new heads, says that training is excellent but of limited value. “Headship is about leadership,” he says. “Much of it involves heavy responsibility and that cannot be taught. Many new heads leave saying they know what needs doing but are too stretched to do it and this is where mentoring comes in, because experience counts.”

*The school has not been identified to avoid prejudicing its advertising