The Government has been accused of needlessly limiting the support available to weak schools by insisting that good and outstanding schools wanting to link up with them must have academy status.
One large county local authority has warned that the policy means the supply of outstanding schools available to help has "well and truly run dry". Heads' leaders also fear it could create a shortage of good schools able to collaborate.
The issue has emerged as a side effect of ministers' plans to tackle underperforming schools by turning them into academies. But only other academies or academy chains are then allowed to sponsor these schools, barring many with top Ofsted ratings and excellent results from formally collaborating with them.
The problem is highlighted in a report, Schools Causing Concern, published by the Association of Directors of Children's Services (ADCS) this month. It warns that "the insistence by the Department for Education that a school has to be an academy to support an academy will prevent some effective school-to-school support".
The report's author, Debbie Pritchard, said she has heard of several instances of this policy limiting the options available for weak schools during her interviews with schools and local authorities. "It seems unhelpful that opportunities for outstanding schools to work with failing schools are being prevented," she said.
Brian Lightman, general secretary of the Association of School and College Leaders, said he was concerned about the policy's impact. "This is about encouraging more schools to convert to academy status, but if they don't, there is going to be a shortage of support," he said. "We would want all outstanding schools to help each other. An overemphasis on the structure of schools could get in the way of us improving our schools system."
Mr Lightman said he knew of one local authority that was encouraging a secondary to convert to academy status specifically so that it could support another secondary in need of help.
Ms Pritchard, a former senior Devon Council education officer, gave an example of an inner-city federation led by an outstanding primary that had already dramatically improved at least three other primaries. It wanted to help a failing primary that the DfE was turning into an academy, but was told it could not unless it too became an academy.
In a second example, the large county local authority mentioned earlier told Ms Pritchard in an email: "Outstanding and good schools are not being allowed to support failing or satisfactory schools unless they become academies."
It added that as soon as the DfE decided a failing school could only recover by becoming an academy, "a huge number of our outstanding and good schools" were eliminated from offering support. "Very few of our primary schools are now looking to convert, so the pool of outstanding academies is really well and truly run dry!" the email continues. Its schools preferred the idea of non-academy formal partnerships, but the government's policy was "driving schools more towards academy chains".
Ms Pritchard's report also found that some heads of good and outstanding schools said "God help us" in response to the "systemic approaches" used by academy chains to tackle failing schools.
Nick Hudson, chair of the ADCS' education achievement committee, said he knew of several non-academy outstanding schools being turned down by the DfE when they offered support for schools in need of significant improvement.
"Is it the progress of children that is taking precedence in these circumstances?" the Wigan Council director of children's services said. "Or is it academisation?"
A DfE spokesperson said: "We want to see academies and maintained schools working together. The academy funding agreement requires that they are at the heart of their community, promoting community cohesion and sharing facilities with other schools and the wider community."
By 1 April 2012, 1,776 academies were open in England.
Of these, 355 (300 of which are secondary schools) were sponsored academies following the original model introduced under Labour.
The remaining 1,421 are converter academies, with a total of 1,838 applications for conversion approved.
Last month, a poll by Reform and the Schools Network found that additional funding was the most common reason for becoming an academy, cited by four-fifths of responding academies.