By Angela Harrison
Education reporter, BBC News
Outstanding schools will be checked only every five years
More schools are failing new-style checks brought in by England's schools' inspectors, it is reported.
The proportion of schools classed as "inadequate" has almost doubled since changes came in last September, says the Times Educational Supplement.
Inspection body Ofsted will not comment on the data but says the new checks have focussed on weaker schools.
Head teachers are calling for an urgent review of the system and say the bar has been raised too high.
The Times Educational Supplement (TES) has analysed the results of inspections carried out by Ofsted since the changes were brought in.
It says only 9.2% of schools have been given the top rating of "outstanding" since then, compared with 19% of those inspected in the academic year of 2008/9.
Since September, the TES says 7.5% of the schools inspected have been classed as "inadequate", compared with 4% in 2008/09.
Ofsted is due to publish a report on the new-style checks next Wednesday and says it cannot comment on the statistics in advance of that.
But the inspection body did say that between September and December, more than 2,000 inspections had been carried out under the new system.
A spokesman said: "It is important to note that the new inspections have been focusing more on weaker schools and this could be expected to have an impact on overall outcomes".
And he added: "We have also made it clear that every time an inspection framework is revised, expectations are raised too. We believe it is right for Ofsted to have these higher expectations on behalf of pupils and parents".
John Dunford, general secretary of the Association of School and College Leaders (ASCL), said the statistics were "worrying".
"Ofsted said that it was raising the bar with the latest inspection framework but we didn't realise they were going to double the height that schools had to jump," he said.
"If these figures match Ofsted's, they are very worrying statistics and show just how much more severely schools have been graded this term."
Under the new system of checks, inspectors now spend twice as long monitoring lessons and more emphasis is placed on exam results.
Schools which are graded outstanding are only inspected every five years while weaker schools are inspected more often.
They are now given just one or two days' notice, although snap inspections can take place when there is cause for concern.
Inspections have also been shortened and now take just a few days.
Head teachers in the ASCL group, meeting for their annual conference in London, were critical of Ofsted.
President John Morgan said: "Raising the bar may have some points in its favour as a strategy but not if it adds to the pressure on schools in challenging circumstances because of the new over-emphasis on raw attainment."
John Fairhurst, head teacher of a school in Brentwood, Essex, said the new short inspections were not long enough for the inspectors "to get the bottom of the context and the way the school is dealing with its challenging circumstances".