Image caption The study looks at how inspection grades have changed after academy status

Schools in England which opted to become academies have improved more quickly than those staying as local authority schools, according to an analysis of Ofsted inspections.

The Department for Education has published a report on how so-called "converter" academies have performed after their change of status.

These account for more than two-thirds of the 3,613 academy schools.

These schools were more likely to improve from "good" to "outstanding".

This analysis looks at what happened to inspection results in 2012-13 in the wake of the rapid expansion of academies, which have become England's most common form of secondary school.

Among England's state sector secondary schools, 56% are now academies. Among primary schools, 11% have academy status.

Higher rating

Academies are state-funded and non-fee charging, but have greater autonomy, such as not having to follow the national curriculum. They were launched in 2002, but grew rapidly under the coalition government from 2010.

Within this category of school the largest number are more than 2,500 converter academies, which opted to become free-standing, directly funded state schools, outside of local authority control.

This report looks at the performance of such converter academies, many of which would have been higher-attaining schools before changing status.

Because these converter academies were already disproportionately likely to be graded good or outstanding by Ofsted, this study looks at how inspection results have changed after becoming academies.

Our reforms are raising standards and giving more parents the choice of a great local state school Michael Gove, Education Secretary

This analysis shows that at both secondary and primary level, converter academies were more likely to have improved their grades and less likely to have moved downwards than local authority schools.

It means that more moved up to good or outstanding or retained a rating of outstanding.

This study does not include "sponsored" academies, which were more likely to have replaced a previously underachieving school. It also does not include schools which were forced to become academies.

But it suggests that the converter academies are moving further ahead.

In terms of GCSE results, this summer's results showed 70% of converter academies achieving the benchmark of five good GCSEs including English and maths, compared with 59% of local authority schools.

Education Secretary Michael Gove said: "This report shows that academies are doing much better than local authority schools.

"Academy status lets teachers get on with the job, free from bureaucratic interference. Our reforms are raising standards and giving more parents the choice of a great local state school."

A Labour spokesman said: 'It is not the legal status of a school that matters most, it's the quality of the teaching in the classroom.

"David Cameron has watered down teaching standards by allowing unqualified teachers into classrooms on a permanent basis. The Tory-led government is neglecting teacher quality for all schools, which is damaging standards across the country as a whole."