There is confusion over why PricewaterhouseCoopers' (PWC) second annual report on the scheme, due to be delivered to the Department for Education and Skills in December, has still not been published. Both parties say they are waiting for the other to finalise the work.
The department chose not to release the consultants' first academies report which warned that the policy, designed to raise standards in disadvantaged areas, could create a two-tier education system based on social class.
It received the report eight months before announcing a pound;5 billion plan to have 200 academies in development by 2010. Its contents were only revealed after the document was obtained by The TES under the Freedom of Information Act.
Since then the latest test results for 14-year-olds showed nine out of 11 academies, independent state schools backed by private sponsors, finished in the bottom 200 schools in England.
Teachers' leaders and MPs are urging the Government to publish the PWC report. They want to see evidence of the effectiveness of academies before ministers press ahead with the expansion plan. Steve Sinnott, National Union of Teachers general secretary, said that sitting on the report suggested there was something to hide.
Ruth Kelly, Education Secretary, has told teachers that the Government "cannot afford to wait" for further evidence on the success of academies as children in deprived areas need a new approach now. Her department said that at the 11 academies where pupils sat GCSEs last year, the proportion gaining five Cs or better rose on average from 21 to 30 per cent.
But this claim is based in part on comparisons with predecessor schools that do not all have the same intake.
Last month the Commons education select committee said: "We fail to understand why the DfES is putting such substantial resources into academies when it has not produced the evidence on which to base the expansion."