More than a third of schools inspected in the second quarter of this year were not good enough, according to official figures.
Of the 1,476 state schools in England visited by inspectors between April and June, 74 (5%) were considered "inadequate", effectively failing to give pupils a decent education, Ofsted statistics revealed. A further 435 schools (29%) were only rated satisfactory.
The schools declared inadequate were either placed in special measures or given a notice to improve.
The figures exclude around 30 schools which were inspected during the second quarter of 2012 but did not have their inspection report published by the end of July when the statistics were collated, said Ofsted. Once these are included, the numbers of schools considered inadequate could rise to around 7%, although this is still a drop on the first three months of the year when 13% of schools visited were rated as inadequate.
The fall may be partly down to a higher proportion of good and outstanding schools being inspected after being flagged under the watchdog's risk assessment systems, said Ofsted.
Under new inspection rules, schools previously rated outstanding are not routinely inspected and those considered good are inspected less frequently, unless questions are raised through the risk assessment process. This could include a change of headteacher, high turnover of staff or queries over results.
The statistics also show that just over one in 10 schools (11%) visited between April and June were found to be outstanding and 55% were good. Around three-fifths of all schools visited in the second quarter (57%) were rated good for behaviour, 26% were found to be outstanding, 16% were satisfactory and 1% were inadequate.
Russell Hobby, general secretary of the National Association of Head Teachers, said: "These figures suggest that Offset's inspectors may, at last, be starting to get the hang of the new framework."
There was anecdotal evidence earlier in the year that gave the union "considerable cause for concern over the quality and consistency of school judgments on which so much depends", he said. "These new figures give us hope that a corner may be about to be turned, and we are pleased to note that the many strengths of our school system are starting to come through.
"We are particularly pleased that Ofsted has clearly demonstrated that persistent suggestions in some quarters that behaviour is poor in our schools and that leadership teams are weak are simply not true. Such myths damage confidence in our school system and get in the way of attempts by school leaders to raise the quality of teaching and learning."