A Medway grammar school is Britain’s second ever to be put in special measures.
Inspectors blamed hugely variable teaching and failed leadership for their verdict on Chatham Grammar School for Boys.
Almost every pupil there meets government targets, but Ofsted said they were simply not improving enough.
Chatham Grammar School for Boys
The shock report has finally been made public more than a month after its existence was highlighted.
Head teacher David Marshall initially fought the findings, which delayed their release - but he then retired suddenly at the end of August.
The official report means the school, which became an academy in 2011, could be shut down if it does not improve.
It is now under temporary leadership from the neighbouring Rochester Grammar School and has been told not to hire any newly-qualified teachers.
Lead inspector Anne Wellham said: “Leaders do not have an accurate view of the academy’s strengths and weaknesses.
Executive principal Denise Shepherd and interim principal Stuart Gardner have been drafted in from the neighbouring Rochester Grammar School
“Their judgements about the quality of teaching are over-generous because teachers’ performance is not checked thoroughly by senior managers and teachers in charge of subjects.”
Pay rises were given too readily, she said, and government “pupil premium” cash was spent on the whole school instead of its most needy members, widening the equality gap.
There was a stark contrast between pupils’ good behaviour in breaks and bad behaviour in class, where their attitudes were “a direct response to the quality of teaching.”
Other concerns were “inconsistent and irregular marking”, so much so that pupils asked their work to be marked by some teachers and not others.
Teaching itself ranged from outstanding to inadequate, with average maths scores, good science scores but poor scores by grammar school standards in English, languages and humanities.
This summer 95% of the school’s GCSE pupils gained five A* to C grades including English and maths, down from 100% last year.
Denise Shepherd, executive principal of the Rochester Grammar School, defended Chatham Grammar’s reputation.
“This is a school that has very good results,” she said. “It’s still very much on a par with local grammar schools across Kent and Medway.”
But she added: “We have to accept the findings of the Ofsted report. Our job is not to criticise and unpick.”
The Rochester Grammar School already does work to improve failing schools. New measures will include monitoring teachers more closely and giving them professional coaching to improve their style.
Ms Shepherd denied claims that teachers’ morale is low. “We have spoken to all members of staff,” she said.
“They’re pleased there’s stability in the school in leadership. I think there would be morale problems if the head had left and there was no leadership.”
Rochester Grammar School head teacher Stuart Gardner, now Chatham Grammar’s interim head, added: “They just want the best for the boys.”
“We have to accept the findings of the Ofsted report. Our job is not to criticise and unpick” - Denise Shepherd
Ms Shepherd said she could not say whether Mr Marshall was forced out, adding: “It’s our first full week on the job.
“I think Mr Marshall has clearly made a decision himself and I really wasn’t privy to those discussions at the time or since,” she said.
Mr Gardner, meanwhile, would not say how many days a week he will be at the failing school, or how long he might hold the position of interim head.
Education adviser Peter Read claimed the school had been caught in a “twin grip” of falling pupil numbers and a Medway test which discriminated against boys.
“I must confess, I am a fan of the school,” said Mr Read. “Without exception, all [parents I speak to] talk about a happy school, one that encourages children to get on and succeed.”
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