academies are on course to deliver value for money to taxpayers despite a host of problems, including low standards in English and maths, government auditors said today.
The mixed report from the National Audit Office also reveals that private sponsors are winning control of the controversial schools at knock-down rates as low as pound;295,000.
The auditors highlight academies' poor sixth forms and their lack of collaboration with neighbouring secondaries. They also say that London benefits disproportionately from the scheme, to the detriment of other deprived areas such as the North West.
The spending watchdog notes the "good progress" academies have made in improving GCSE results, which are rising at a faster rate than in other schools. But it questions whether improvements will be sustainable once start-up funding is phased out, good heads are in short supply and expensive, and innovative buildings need renovating.
Sir John Bourn, head of the audit office, said the pound;5 billion programme was raising the achievement of deprived pupils. "The challenge for academies is to sustain improvements while spreading the benefits more widely in their communities," he said.
Alan Johnson, Education Secretary, said: "Academies work - and are worth it."
The report looked at the 27 academies opened by September 2005 and found that a year later only 11 had received the pound;2m the Government originally specified sponsors should pay to control the schools.
Nine had received payments of less than pound;1 million. And Sir Harry Djanogly had not paid anything at all to sponsor Djanogly academy, Nottingham, because of his contribution to its predecessor city technology college.
Some sponsors had agreed to pay in instalments, but in four cases - two involving the United Church Schools Trust - the payments were behind schedule, by an average of around pound;200,000.
The report found that academy GCSE results were well below the national average, but improving faster than other types of secondary. Their contextual value added scores were also higher.
But their predecessor schools had also seen a sustained improvement in results. And the auditors did not take into account academies' use of vocational qualifications to boost their GCSE scores. Paul Wright-Anderson, manager of the auditing team, said: "That is what the system allows and we are not here to comment on it."
The report found permanent exclusion rates in academies nearly four times higher than the national average, but said they "do not appear to impact unfairly on the performance of neighbouring schools".
The Government has always claimed that academies receive the same funds for running costs as other schools. But the auditors discovered that the 12 academies opened by 2003 had on average each received an extra pound;1.6m in start-up funding by 200506. This amounted to an extra pound;460 per pupil per year and was "substantially higher" than the average pound;750,000 extra start-up funding paid to other under-performing secondaries that have been given a "fresh start".
Two-thirds of academies were still receiving start-up funding in their fourth year, the auditors found. They recommend it should cease after three.
The report found that academy sixth forms had "not performed well so far"
and it stressed that a strong business case should be made before more were opened.
The auditors said that academy heads were a "vital ingredient" to their success, but that there was a risk of a shortage as the programme expanded from 200 to 400 schools.
The report came as a National Governors' Association survey found that 95 per cent of local associations were opposed to the expansion, with 80 per cent agreeing that sponsors' contributions were too small.
Meanwhile, campaigns against plans for two more academies in London are gaining ground, with public meetings being held in Wembley on Wednesday and Camden on March 5.