Most people seem to like Thornhill Community Academy. When the school featured in the television series Educating Yorkshire, viewers wrote to ask if staff members were single. A TV critic proposed that the teachers should all be given knighthoods. The Department for Education even decided to use English teacher Matthew Burton to front a teacher recruitment campaign.

Ofsted, however, disagrees. Thornhill, in West Yorkshire, has been told that it requires improvement.

The school was inspected last month for the first time in five years. Ofsted said it was “not good”, because attainment at GCSE last year was lower than it ought to have been, particularly in English and maths.

Teaching has “not been precise enough” to ensure that students achieve good exam results, the report says, with some classes failing to meet the needs of the most able students.

“Some students lack skills in understanding the meaning of texts and in producing extended writing,” inspectors add. “This limits their success in exams.”

But headteacher Jonny Mitchell received the news with equilibrium. “It’s the first time that I’ve led a school through an Ofsted inspection,” he told TES. “I’d heard horror stories about the attitudes of inspectors. But they were a very positive advert for Ofsted. There are no sour grapes there. Apart from the outcome, it was a wholly pleasurable experience.”

Educating Yorkshire, Channel 4‘s fly-on-the-wall documentary series about the school, was watched by more than 4.5 million viewers at its peak. Even initially sceptical TV critics were won over by the end of the series, with its poignant portrayal of student Musharaf Asghar’s struggle to overcome his stammer.

However, GCSE results fell sharply at Thornhill last summer, with only 17 per cent of pupils achieving five A*-C grades including English and maths. The previous year, 54 per cent had attained the same level.

Mr Mitchell points out that some pupils’ grades were not included in this year’s figure because of a change in the way results were measured. GCSE English results did not count towards the school’s scores if students had also sat a GCSE in English literature beforehand.

“I remember results morning in August, thinking, `Oh my God, we’ve dropped’,” he said. “It’s very rarely that I indulge in Schadenfreude, but when I saw the results for the rest of the local authority, I thought, `It’s not just us.’ And results have dropped in other local authorities, even more than here.”

He acknowledges that Ofsted was correct to say that some pupils did not make sufficient progress. “We’re not naive and unpragmatic,” Mr Mitchell said. “I don’t think we could disagree that our achievement in 2014 required improvement.

“But it’s five years since we were last inspected. It’s cruelly ironic that in four of those five years we were improving.”

Inspectors also recognise the school’s positive features. The report says that Mr Mitchell and his senior leaders have “established a positive culture for learning in classrooms and the school”. Behaviour, too, is “good and managed well”, and “students’ spiritual, social, moral and cultural development is good, and prepares them well for life in modern Britain”.

The findings were welcomed by Mr Mitchell. “There have been so many, many positives about the last four years that I’ve been here. The staff are uber-committed,” he said.

And the decision to allow TV cameras into school corridors was not to blame for the inspection result, Mr Mitchell insisted. “The programme has been nothing but positive,” he said.

“It had a positive effect, in terms of the working environment, the atmosphere. I don’t think it can ever be claimed that it was a distraction from our core purpose.”

Mr Mitchell is planning to leave Thornhill this year to take up a headship at the nearby Co-operative Academy of Leeds; his successor will be appointed at the end of the month.

“But it doesn’t make me feel any less cheesed off, because I’m leaving,” he said. “We want to turn that `requires improvement’ into a `good’ as soon as possible.” He paused. “Unless they prat around with the system again.”