More than 50 failing schools have not been converted into academies 18 months after the government issued an order on them to do, according to Ofsted.
New figures show there are 51 schools that had been given a directive academy order (DAO) after being rated "inadequate" by inspectors but which have still yet to become an academy a year and a half later.
And 39 of these schools have been waiting to convert to academy status for more than two years.
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However, the data also shows that nearly 30 schools have managed to go on to get an inspection rating better than "inadequate" without being turned into academies.
The figures show the challenge the Department for Education is facing in converting some failing schools into academies.
Schools are given orders to convert to academy status by regional schools commissioners if Ofsted rates them as "inadequate".
Ofsted said the number of schools that have remained open “for a very long time” after being given an academy order has increased slightly in 2018/19.
Despite this, the figures published by the inspectorate today show that there has been an overall decline in the number of schools that are still open with a DAO. There were 168 in the last academic year, compared with 220 the year before.
Ofsted has said that if a school remains open for a long time with a DAO, the inspectorate can decide to inspect it again.
Of the 168 schools that are still open with DAOs, 97 have had another full inspection.
The Ofsted figures published today show that 27 of these have improved to "good" or requires "improvement".
The figures published by Ofsted today also show that only 16 per cent of "outstanding" schools kept their top rating in the last academic year after re-inspection.
More than half (56 per cent) declined to "good", 23 per cent to "requires improvement" and 5 per cent to "inadequate".
A higher proportion of primary schools, previously exempt from inspection owing to their "outstanding" status, declined in their rating than secondary schools: at 87 per cent compared with 76 per cent.
Ofsted can reinspect "outstanding" schools if it has concerns about standards or safeguarding. Plans announced this year by the government to remove the exemption on all "outstanding" schools from being routinely reinspected have yet to be enacted.