A government initiative to vet academy sponsors has been damned as "secretive" after it emerged that decisions on suitability will be made behind closed doors.
The accreditation scheme for academy and trust school sponsors is supposed to provide a robust check of organisations that want to run schools.
However, it has come under fire for deciding only to refer groups planning to run three or more schools to an external panel. The advisory panel will have no say on organisations that want to run one or two schools.
The composition of the advisory panel has also been criticised for including an academy sponsor among its members, raising fears that it will not be properly independent.
The concerns about how sponsors are chosen and accredited follow an announcement by Gordon Brown last week that parents will be able to trigger a ballot if they are unhappy with standards in their local schools.
If a "significant" number of parents vote in favour, groups that have passed the new accreditation tests will be able to take over the running of the schools, the Prime Minister said.
But Mary Bousted, general secretary of the Association of Teachers and Lecturers (ATL), said that the system failed to provide a properly robust check. All final decisions on potential sponsors are still made by the Schools Secretary, Ed Balls.
"The process at present is worryingly secretive," she said. "We looked to the accreditation process to establish strong external validation for potential sponsors, but if you want to run one or two schools, nothing has changed.
"And having an academy sponsor on the panel is a case of I'll scratch your back if you scratch mine.
"This is a worthless exercise being used to cloak the expansion of academies in an aura of respectability, while changing nothing."
John Chowcat, general secretary of the Association of Professionals in Education and Children's Trusts, said there was "no logic" in having external checks on some groups, but not others. "The accreditation process for the organisations should be transparent and run independently of the Government - these are the fundamentals," he said.
As reported in The TES, an initial pledge to ban non-educational organisations from being the sole sponsors of academies was dropped after a consultation.
The Department for Children, Schools and Families altered its plans after sponsors complained that the changes risked stifling innovation. A spokesman said: "We think it is right that groups, who want to lead three or more schools, must undergo additional scrutiny.
"That is why their proposals are reviewed by an independent accreditation advisory group made up of a range of education experts."