The independence enjoyed by academies will fail to deliver long-term improvements in exam results, research which followed the fortunes of former grant-maintained schools has found.
Rebecca Allen, of London University's Institute of Education, found that early increases in pupil performance were not sustained in the schools which, like academies, won significant powers from local authorities and extra funding.
One in six schools became grant-maintained between 1989 and 1997. The policy was abandoned by Labour, but many retained similar freedoms by becoming foundation schools.
An analysis of exam results shows these schools have performed no better than other similar schools in the long term.
"The assumption that autonomy from local authorities is desirable is implicit in many strands of government reform such as the academies programme and trust schools legislation," the research said. "This study suggests there is no reason to believe that these new policies in autonomy will lead to sustained improvements in exam performance."
Schools that wanted to become grant-maintained had to win a parental vote. The research compares schools that narrowly won their votes with schools that narrowly lost and therefore stayed as community schools.
Grant-maintained schools improved their performance immediately following the switch. But results later slipped back to the same level as schools that tried to become grant-maintained but failed.
This contradicts government exam league tables, which showfoundation schools outperform community schools. Last year 54 per cent of pupils in community schools achieved five good GCSEs compared to 64 per cent in foundation schools.
Changes to the way a school is run can lead to improvements as it gives teachers a fresh focus on improving standards, the report says. "We see this phenomenon in many of the new academies. However, in the long-term, this higher level of effort directed at exam outcomes relative to other schools starts to decline."
The Government claims that the independence academies have is key to their ability to turn around poor performance. However, Ed Balls, the Children, Schools and Families Secretary, has more recently called for academies to work more closely with other schools in their areas.
Results from academies have been mixed. An evaluation by consultancy PricewaterhouseCoopers earlier this year found exam results were improving more quickly than national averages, but there were significant differences between schools.
Jerry Bartlett, deputy general secretary of the NASUWT, said: "I'm not surprised. Our assessment of academies is that improvements made are due to initiatives already in place while the schools were in local authority control."
Accolade for academies, page 26.