A defiant head teacher whose school suffered a bruising Ofsted report is accusing the watchdog of operating a “crude academic race which for many children is unwinnable”.

Canterbury High School has lost its ‘good’ rating and been downgraded to ‘requires improvement’ after inspectors swooped earlier this year.

In a report published this month, Ofsted based its conclusion on pupils’ overall exam results in 2014, which were well below the national average.

Phil Karnavas, head of the school in Knight Avenue, has hit back, arguing that judging a school solely on academic prowess will inevitably see some favoured over others.

“We have always been candid that our GCSE outcomes last year – at 37% on ‘first entry’ – were disappointing. We can explain this but we have never sought to excuse or spin it,” he told KentOnline.

“But if schools are only as good as their last set of results and if national averages are to be used as the benchmark then, in a fully selective area, non-selective schools will struggle.”

Ofsted had previously given The Canterbury Academy a favourable report praising the school in many areas, particularly the performing arts.

But in its latest report inspectors appear less than impressed.

The report says: “The quality of teaching over time is not consistently good across all subjects or within some subject areas such as science and humanities.

“Although there is some excellent practice, for example in performing arts, pupils’ progress in several areas, including humanities subjects, is not good enough.”

Inspectors also highlight deficiencies in some pupils’ reading and writing skills, commenting: “Teachers do not always identify or follow up issues of poor spelling and grammar and, as a result, some pupils’ literacy remains too weak.

“Not enough challenge is offered to more-able pupils, which means that they are not making rapid enough progress, including in English.”

In its conclusion, the report states: “Pupils’ overall achievement in 2014, including in English and mathematics, was much lower than that seen nationally.”

This conclusion appears the basis for the downgrading.

Mr Karnavas has defended his teachers and pupils, pointing out that the inspection process does little to recognise and achievement beyond results alone.

He said: “There is much in the report that is very positive about the school’s culture and ethos , sport, performing arts, the diversity and range of opportunities, extra curricular activities, employability, social development, guidance and support, welfare, vocational provision, conduct, etc.

“But none of this means that the school can be good.

“I think inspection is important. But I have some doubts about this model.”

Mr Karnavas also states that the inspection outcomes can be largely arbitrary.

“It is widely accepted that there is an element of chance in every Ofsted inspection; in many ways, it depends who you get and when you get them,” he said.

“This leads to Ofsted judgements across areas which appear bewilderingly inconsistent - some schools with better results get worse reports and some schools with worse results get better ones.”

In a parting shot at the watchdog, Mr Karnavas adds: “Education should value academic achievement but it should also value other forms of achievement.

“It is simply wrong that education is allowed to degenerate into a crude academic race, which for many children will be unwinnable.”