academies are improving exam results more quickly than similar schools and national averages, a government-backed report has found.

The independent state schools are beginning to attract brighter pupils and are offering a wider range of vocational courses, the annual review by PricewaterhouseCoopers (PwC) said. However, there are significant differences in performance between schools.

There are also concerns about poor behaviour and attendance, with a small number of schools continuing to have high levels of permanent exclusions, the report said.

The findings come in the same week that the TUC called for the expansion of the academies programme to be stopped.

By September, there will be more than 80 academies open in 50 local authorities, with plans to open a total of 400 across England.

The TUC urged the government to hold an independent review of all school improvement initiatives, such as Excellence in Cities and London Challenge.

This would allow a better understanding of the merits of academies, it said. It also wanted the schools to be put under local authority control as a way of making them more accountable. The PwC report found better overall performance in tests by 14 and 16-year-olds, but big variations between schools.

Results in key stage 3 tests for academies that opened in 2003 have increased by an average of 21 percentage points. However, in one school results were down by 9 points between 2003 and 2006. In another, science tests were up by 55 points. The number of pupils getting five good GCSEs in the same academies was up by 13 percentage points, compared to six nationally.

The rapid improvement in results in some academies is because of greater use of vocational courses and GNVQs and the differences in attainment can also be partly explained by the admissions arrangements of the schools. Many are opting for a fair banding system to attract a wider ability range, the report said. As school performance improves, more middle-class parents are prepared to choose them.

The Department for Children, Schools and Families was encouraged to take a close look at academies using fair banding. “This is to ensure that there are no overt or covert barriers preventing the most disadvantaged pupils from accessing academies,” the report said.

The average ability of pupils when they start at academies is still lower than in similar schools, but it is increasing.

The TUC said that Gordon Brown becoming Prime Minister provided a “perfect opportunity” to take stock of the impact of academies on standards. It also called for full union recognition rights for teachers at all academies.

Gordon Brown, Prime Minister, has signalled a change in the academies programme, encouraging greater sponsorship from public sector organisations. To get universities involved, he has waived the need for them to provide pound;2 million in sponsorship. New academies will have to follow the national curriculum in core subjects, which existing academies are free from.

At Capital City academy in Willesden, north London, an average of 25 per cent of pupils have gained five GCSE grades A to C since becoming an academy in 2003. This is more than double the 12 per cent it was achieving before.

Philip O’Hear, headteacher, said the independence of being an academy was a key reason for its improvement. “The fact that no one else is responsible for how we do concentrates the mind and means we feel a great deal of moral pressure to perform,” he said.

“Expanding the programme rapidly carries a risk of diluting the impact. Only time will tell if having 400 academies will work. But not to risk it seems morally reprehensible to me.”