Sir Michael Wilshaw has written to Ofsted’s inspectors to tell them to stop judging schools and teachers on their style of teaching.

The chief inspector of schools has issued the missive to all inspectors, spelling out Ofsted’s existing policy that the school watchdog should not be prescriptive about “preferred teaching styles”.

The stern message comes at a time when Sir Michael has become embroiled in a row with the Department for Education and right-leaning think tanks over what he has deemed as “right-wing attacks” against the inspectorate.

In an interview with a Sunday newspaper, Her Majesty’s chief inspector said he was “spitting blood” after learning that both Civitas and Policy Exchange were working on reports questioning the future of the inspection agency.

Sir Michael even suggested that supporters of education secretary Michael Gove were involved in undermining his work since becoming head of Ofsted, forcing Mr Gove to issue a denial.

And in the equally brusque internal communiqué, seen by TES, Sir Michael has had to reiterate Ofsted’s own policy, telling his inspectors that they should only be concerned with the impact that teaching has on learning, not on certain teaching styles.

“Nevertheless, I still see inspection reports, occasionally from HMI, which ignore this and earlier guidance and, irritatingly, give the impression that we are still telling teachers how to teach,” he writes.

The former headteacher has even set out examples where inspectors are still including comments about different methods of teaching, which he said should not be included in any inspection reports.

They include comments such as, “Insufficient time was given to collaborative learning” and “Weak teaching is characterised by teachers talking too much”.

The memo comes just a week after TES reported that at least half a dozen school inspection reports had to be changed after they were published because they contravened Ofsted’s own guidance on teaching styles.

Among them was Durand Academy, lauded by Mr Gove as an “outstanding school doing a wonderful job”, but unexpectedly downgraded to “good” by Ofsted before Christmas.

In his note, Sir Michael urges his inspectors to “break away” from an “orthodoxy of inspection report-writing” that has grown in recent years.

“In summary, inspectors should report on the outcomes of teaching rather than its style,” he concludes. “So please, please, please think carefully before criticising a lesson because it doesn’t conform to a particular view of how children should be taught.”

His comments refer to new guidance published in the run up to Christmas, which was widely welcomed by the teaching profession. 

Brian Lightman, general secretary of the Association of School and College Leaders, said that Sir Michael’s internal message was timely. 

“The inconsistency of inspector teams has been an ongoing problem for a long time so we warmly welcome the very clear statements that were included in the sub-guidance,” Mr Lightman said. 

“This letter is obviously following that up and we’re very pleased the chief inspector is continuing to impress upon his inspectors the importance of consistency.”