Ofsted is using an unrepresentative sample of schools to set the bar for how it will grade schools under its new inspection framework, Tes can reveal.

The inspectorate has said it will use the findings of pilot inspections to try to ensure the overall proportion of school inspection grades remains roughly the same as they are now when its new regime is launched from September.

So far, just 54 pilot inspections have been conducted, of which “nearly all” were of schools “judged to be ‘good’ or ‘outstanding’”. Another 120 are planned but Ofsted says they are “unlikely” to include any “inadequate” schools. 

Ofsted did not respond when asked whether the pilot schools would be representative in terms of levels of pupil disadvantage.

Inspector training for the new framework is being based on the results from this sample, which it also plans to use to calibrate grades to ensure the overall profile remains the same.

Ofsted’s director of corporate strategy Luke Tryl indicated that Ofsted would also make allowances during the first year. 

“We know that for many schools their plans for next year’s curriculum is already set in stone,” he told Tes. “There will be a recognition in the handbook that particularly in the first year we are more interested in the trajectory a school is on in terms of its curriculum.

“We don’t want schools rushing out and signing up to a Pixl approved curriculum. That is not what we want to achieve through the new inspection framework. There will be a recognition that schools need to be given time.”

However, Ofsted is facing questions about how it can ensure the number of good and outstanding schools remains steady under the new system.

Commenting on social media, teacher Mark Enser questioned whether Ofsted would grade a set number of schools as being “good” irrespective of the inspection findings.

When asked by Tes what Ofsted would do if there was a significant change in school report outcomes under the new framework, Mr Tryl said the inspectorate was confident this wouldn’t happen.

He added: “We have experience of going through multiple framework changes and ensuring that we set the bar in the right place.

“Through inspector training, we ensure that inspectors understand what the different grades might look like. Through our pilots we are able to see what profiles inspectors are giving against current judgements, we can then recalibrate training accordingly.

“That is why we are conducting so many pilots and investing so much in inspector training.

“At the same time, our reports go through a quality control process to make sure the right judgements are being given.”

Mr Tryl rejected suggestions that Ofsted was using quotas or norm referencing to hold inspection grades steady.

He added: “Over time if we see a significant improvement or, and we hope we do not see this, a significant deterioration in schools then we will report on that but what we are saying is that there shouldn’t be a significant change as a result of the transition to a new inspection framework.”

However, Nick Brook, the deputy general secretary of the NAHT headteachers’ union has questioned whether Ofsted should be trying to predetermine the overall spread of inspection results.

He said: “Some leaders may take comfort from hearing that the proportion of schools to be judged good or better will not change between frameworks, however, this does beg some bigger questions about inspection itself. 

“Inspection should surely be a criterion-based activity. To put it simply, Ofsted will set out their view of what a good school looks like within the framework and handbook and inspection then determines how many schools meet those criteria.

“It seems odd to say the least to suggest that the proportion of schools that will be judged as good under a brand new framework has in some way been pre-determined.

“If you change the rules of the game, you might reasonably expect results to change, too.”

“I think trying to ensure that a particular number of schools are good or outstanding is a dangerous precedent to set. It sets us on a dangerous path where inspectors’ findings are not what is determining the outcomes.”

Ofsted will announce plans for an overhaul of how it inspects schools tomorrow with an increased focus on the curriculum.

It said it wanted to give schools judged to be “inadequate” the “space and time to focus on improvement rather than having to dedicate resource to the piloting”.

Mary Bousted, joint general secretary of the NEU teaching union, said: “Ofsted is in a problem of its own making. It is introducing a major change in the way it inspects schools and not giving schools enough time to adapt to it.

“It will consult for 12 weeks and then schools will get the framework at the start of the summer term and have one term and the summer holiday to prepare for it.

“What Ofsted is doing now is an admission that the first schools who are inspected under the framework are guinea pigs. Ofsted should have given schools longer to adjust. There will be questions now about whether it will be easier for a school to get a ‘good’ at the beginning of the new framework than it will be in, say, two years’ time.”

Ofsted’s new inspection regime is set to place more emphasis on curriculum and give less weight to exam results.

The inspectorate is replacing the inspection grades for teaching and learning and also pupil outcomes with a new quality of education grade.

This will look at both exam and test scores along with the intent, implementation and impact of a school’s curriculum.