Becoming an academy has little effect on primary schools which are already good, a new analysis looking into the effects of conversion has found.
But the analysis from SchoolDash does show that previously poorly performing sponsor-led academies improve markedly after they gain the status.
The research comes as pressure grows on Nicky Morgan, the education secretary, to withdraw plans to force all schools to become academies.
Russell Hobby, general secretary of the NAHT headteachers’ union, said earlier this week that the Department for Education should “press the pause button” on the plans and the County Councils Network, a largely Conservative group of 37 local authorities, has warned that the plans would not lead to higher standards.
The research from SchoolDash looked at the 2015 results of the 807 primary schools which chose to convert between 2010 and 2012.
Timo Hannay, founder of SchoolDash, said that 84.9 per cent of pupils in these academies got the expected level 4 in reading, writing and maths, compared with 83.7 per cent of pupils in similar local authority schools and 81.8 per cent in all local authority schools.
He concluded that while pupils in the convertor academies do better than those in local authority schools, the gap between academies and local authority schools with similar intakes is much smaller. He said this meant that most of the difference between local authority schools and academies was due to differing pupil characteristics, rather than the change in school structure.
'Good before they became academies'
Mr Hannay also looked into whether there had been a change in the performance of the schools over time after they became academies. He found that the convertor academies had done better at getting more pupils to the higher level 5 in reading, writing and maths but the gap between academies and local authority schools in helping pupils achieve the expected level 4 had shrunk.
“Primary converter academies do indeed seem to be good schools. But they were good before they became academies and there’s very little evidence that conversion has done anything to improve – or indeed hinder – their average academic performance,” writes Mr Hannay.
For sponsor-led academies – which have been compulsorily removed from local authority control because of historic underperformance – the gap in performance between these primary schools and local authority schools with similar intakes has narrowed since they were converted.
Mr Hannay found that while sponsor-led academies do underperform other schools, they have become “noticeably better” in a relatively short time following conversion.
He said: “The challenge for those who support compulsory academisation, is to explain why a good school should be forced to convert against its wishes if there are unlikely to be any tangible academic gains. And the challenge for those who oppose it is to explain how else they would reduce the disparity between the best and the worst schools in the country, a gap that is still far too wide.”
A Department for Education spokesperson said: “Our education reforms are raising standards and 1.4 million more children are in good or outstanding schools. Our White Paper reforms are the next step in ensuring every child has access to an excellent education by putting control in the hands of the teachers and school leaders who know their pupils best.
"We want to work constructively with the sector to deliver this and ensure standards continue to rise. The 2015 results show that primary sponsored academies open for two years have improved their results, on average, by 10 percentage points since opening, more than double the rate of improvement in local authority maintained schools over the last two years. International research shows that autonomy within a framework of strong accountability raises standards.”
Want to keep up with the latest education news and opinion? Follow TES on Twitter and like TES on Facebook