While the 2 per cent drop over the last 12 months in the number of schools rated outstanding by Ofsted, as recorded in this week’s annual report, would normally be enough to prompt an orgy of hand-wringing and finger-pointing, the latest batch of statistics published by the watchdog is somewhat different.

The reason is that, since May last year, previously outstanding schools have been exempt from routine inspections, a fact that interim chief inspector Miriam Rosen - keeping the seat warm until superhead Sir Michael Wilshaw arrives in January - was quick to point out at the launch of the report on Tuesday.

The sample of schools scrutinised, therefore, focused on lower-performing institutions, with the best-performing schools largely left to their own devices. This accounted for the slight drop in the number of schools achieving the top grade, Ms Rosen said.

Of those schools previously graded outstanding, only institutions that suffered a significant dip in attainment were visited by inspectors. Education secretary Michael Gove has argued that the policy leaves the top schools “free of that burden” and allows Ofsted to “more effectively focus” inspectors’ work.

But concerns about the exemption have been widely voiced, not least by former chief inspector Christine Gilbert, who spoke in January of her “anxiety about not inspecting those schools routinely”.

And, in this year’s annual report, it seems those fearful prophecies have, at least in part, come to pass. Of the outstanding schools that Ofsted did inspect in 201011, 40 per cent saw their overall grade drop. Even more worryingly, three schools suffered the ultimate fall from grace, seeing their rating slip from outstanding to inadequate in one fell swoop; 11 more schools dropped two levels to satisfactory.

“In the three schools that declined to inadequate, pupils’ achievement had fallen substantially, the quality of teaching was no better than satisfactory and inspectors identified major weaknesses in both governance and safeguarding procedures,” the report said.

In most cases, this was caused by a change in senior leadership, problems with the “stability of their staffing” or a change in the profile of the school’s intake. “This underlines the fact that a previous track record of success is no guarantee that schools will continue to flourish,” it added.

“It’s a risk,” said Brian Lightman, general secretary of the Association of School and College Leaders. “No school is immune from the need to improve further. The idea that there is no room for further improvement in outstanding schools is misguided. All schools leaders know this and can benefit from an external perspective.”

However, he expressed concerns about the “highly variable nature of inspections” and the fact that a school’s grade is based on “a snapshot from a very short visit”.

“It tries to achieve a vast number of conclusions from a very thin evidence base,” Mr Lightman added.

Schools minister Nick Gibb also hit out at “underperforming schools making painfully slow improvements”.

“It is worrying that Ofsted finds that 800 schools are stuck steadfastly at a satisfactory rating in inspection after inspection ... And outstanding or good schools cannot afford to take their foot off the pedal simply because they have had a strong inspection result,” he said.

Sue Gregory, Ofsted’s national director of inspection delivery, told TES that the body’s “robust” risk-assessment process - which involves looking at pupils’ attainment and progress levels, and listening to concerns raised by local authorities and parents - has been designed to identify outstanding schools where standards are slipping.

“If we think a previously judged outstanding school is showing signs of a decline in performance, we’ll schedule it for an inspection,” she said. “We inspected 163 schools last year which were judged to be outstanding; 40 per cent of those declined, which indicates that we were right to go back and re-inspect them.”

Other notable statistics in the report included the revelation that just 3 per cent of teaching in secondary schools - and 4 per cent in primaries - was rated outstanding. The report focused on the “stubbornly satisfactory” schools that had received the same grade for two or more consecutive reports, and made up 14 per cent of the schools inspected.

“That isn’t good enough,” Ms Gregory said, adding that “stuck” schools should focus on improving their lesson planning, assessment and the interaction between staff and students if they wanted to drive up their teaching grade.

She highlighted as a benchmark for excellence the achievements of the 85 schools in the most deprived parts of the country that have been graded outstanding. “A key feature of these schools is they are absolutely, unremittingly relentless in focusing on the consistency of what they do. They have a shared vision, shared moral values, and leaders and middle managers working together to make sure they have an entirely consistent approach, and that no barriers are too great,” she said.

This effusive description certainly gives headteachers an ambitious goal to aspire to. For those who have already got an outstanding rating under their belt, it serves as a timely reminder of the standards they are expected to uphold.

14% of schools were judged satisfactory in their last two or more consecutive inspections

SCHOOLS RATED OUTSTANDING FOR QUALITY OF TEACHING

Primaries 4%

Secondaries 3%

Special 15%

Pupil referral units 8%

Overall 6%

20% of schools previously rated inadequate were found to be good or outstanding

The fifth of schools serving pupils from the most deprived backgrounds are four times as likely to be judged inadequate as the fifth serving those in the least deprived areas.

87% - Schools where pupil behaviour was rated good or outstanding.