Top headteachers say they are being "penalised" by Ofsted for doing what the government wants and helping to turn around struggling schools.
Prime minister David Cameron, chief inspector Sir Michael Wilshaw and education secretary Nicky Morgan have called on England's best headteachers to use their talents to improve more than one school.
But when assessing the effectiveness of their work, Ofsted gives them credit only for what happens in their own school. Headteachers who have seen their leadership rating drop in spite of their efforts to "transform the educational landscape" claim they are being unfairly penalised for working to drive up standards elsewhere.
They warn that the high-stakes inspection regime has created a "serious barrier to system leadership", adding that concerns about the impact of a poor Ofsted grade could deter leaders from taking on additional responsibilities.
Clive Mathew, headteacher of the John Henry Newman Catholic School in Stevenage, said his leadership team had worked "seven days a week for the first six months" to pull a nearby school out of special measures.
But despite this effort, his school's leadership grade dropped in its last Ofsted report. "Why would anybody work with another school?" Mr Mathew asked. "If you want people to do this then you have to acknowledge it in some way.
"The current framework doesn't allow for executive headship and the support for other schools to be recognised. So you are on to a losing wicket."
Brian Lightman, general secretary of the Association of School and College Leaders (ASCL), said: "We absolutely must make sure that schools have incentives to support other schools, and if they are penalised for doing that then it is the inspection system that needs to change."
In September, Sir Michael told TES that all schools should be forced by law to join a cluster or federation led by a new cadre of "exceptional" headteachers. "You say to the outstanding heads, `You're going to get more money for doing this, you'll be judged exceptional by Ofsted'," he said.
But the watchdog's inspection handbook stresses that school leaders' work elsewhere "will be noted by inspectors but should not inform the judgement on the leadership and management".
An Ofsted spokesperson told TES: "It is right that for the school being inspected, judgements on leadership and management are based firmly on the evidence inspectors find within a school and its own particular circumstances."
The number of executive headteachers - leaders who have responsibility for more than one school - has risen dramatically over the past decade. According to the Department for Education, there were 25 in 2004 and 450 in 2010.
Speaking at the ASCL annual conference in London last weekend, Ms Morgan said the government was keen to encourage school leaders to "work together more closely to share expertise and help others improve".
At the same conference, shadow education secretary Tristram Hunt said that, if elected, the Labour party would create a "dedicated school leadership institute" to help headteachers share best practice.
Last month, Mr Cameron called for the best headteachers to have influence over more schools. He said "bog-standard" schools that failed to improve should have to "let experts come in and help [them] - people who have a track record of running great schools and turning around failing ones".
Andrew Hutchinson, headteacher of Parkside Community College in Cambridge, became one such "expert" when he took over nearby Coleridge Community College, which was struggling. Now executive headteacher of the Parkside Federation, he has also helped another two secondaries in Suffolk.
In its most recent inspection, however, Parkside's rating for leadership and management was downgraded from outstanding to good.
Mr Hutchinson wants Ofsted to give more recognition for wider leadership roles. "David Cameron and everybody else is talking about the need for successful heads to transform the educational landscape," he said. "That's great, but it would be nice to see that actually inform the judgement of those schools."
Russell Hobby, general secretary of the NAHT headteachers' union, said that where schools operated in trusts and federations, Ofsted judgements on leadership and management should be shared across the group.
"This would incentivise collaboration," he added. "Ofsted can act as a serious barrier to system leadership, which carries a price. You have got to back these schools up. Nothing you can do in education is without a cost, and time spent on helping another school is time not spent in your own school."
`We were working seven days a week'
At the John Henry Newman Catholic School in Stevenage, the leadership rating delivered by Ofsted has dropped from outstanding to good.
Headteacher Clive Mathew is angry that this has occurred despite improvements in results at the school and the achievement of his leadership team at another secondary.
The team helped to take Nicholas Breakspear Catholic School in St Albans - where Mr Mathew is now executive headteacher - out of special measures within a year. But Mr Mathew says inspectors told him they could not consider the work done there.
"We are penalised in as much as the leadership grade doesn't take into account the work you have done in both schools," he says. "My leadership team were working seven days a week for the first six months.
"It was crippling. We gave up our own lives and now we are being told that we are `good', despite all that evidence.
"I would say you must be doing an outstanding job to be running two schools and both of them to have made significant progress."