Plans to bring a teacher perspective to school inspections in Wales are under threat because not enough people are volunteering to take part, according to schools.
Inspection agency Estyn says it is pleased with the number of people training to be peer assessors, and expects them to be involved in more than half of this term's inspections.
But 12 months after the launch of the "peer assessor" scheme, schools are saying they are not prepared to release teachers - and teachers are reluctant to sacrifice precious time with their own pupils.
Estyn's new inspection framework, introduced last September, envisaged having a suitably trained senior teacher on every school inspection team, to help tap into the expertise of practising professionals.
Hel ne Mansfield, head of Croesyceiliog comprehensive, Cwmbran, was expecting a peer assessor on her school's inspection in March. Estyn says it did not have one because the agency only introduced them from the second half of the summer term this year.
Mrs Mansfield believes that schools are not prepared, or able, to allow the initiative to eat into their time without recompense.
"If one of my deputies had to be out for the day someone else would have to do her job, and that puts a lot of pressure on us. I would be very surprised if we were an unusual case."
Anna Brychan, director of the National Association of Head Teachers Cymru, said it was difficult to see how the scheme would work unless extra funding outside of the school budget was made available.
Estyn does not fund cover for peer assessors, although individuals can apply to the General Teaching Council for Wales for professional development bursaries to cover their absence while on training courses and their first inspection.
"It would be a desperate shame if it didn't work, but the reality has not matched up to what was a good idea in theory," she said.
"We know of people who want to do it but schools are finding it increasingly difficult to release senior staff."
There has also been very little take-up across Blaenau Gwent, according to Dr Brett Pugh, chief education officer.
"The problem is that it's on a volunteer basis and every school is going to have to replace a member of staff to allow a teacher to do an inspection," he said.
But an Estyn spokesman said nominations for peer assessor training in Blaenau Gwent, from 21 per cent of schools, were only slightly down than for Wales in general (25 per cent).
He added: "Estyn currently has 236 peer assessors trained for deployment on inspections in schools. Of the 33 school inspections in the second half of the summer term, 14 had a peer assessor deployed to them (42 per cent) "Of the 102 school inspections planned for this autumn, 60 will have a peer assessor (59 per cent)."
Geoff Brookes, deputy head at Cefn Hengoed comprehensive, Swansea, trained as a peer assessor in February this year. He says he is looking forward to putting something back into the system.
"There has always been a concern that there is a distance between schools and inspectors. Having teachers involved brings realism to the process.
"They are the ones rooted in the reality of underfunded schools and know what the issues are."