A grammar school where 100% of pupils met GCSE targets is contesting what is said to be a critical Ofsted report.

Chatham Grammar School for Boys was inspected two weeks ago as part of a 10-school blitz, which Ofsted launched to probe Medway’s poor primary school results.

It has now received a draft report and the findings are understood to make grim reading.

Multiple sources have told KentOnline that inspectors are proposing to rate the school as “inadequate”, the lowest grade.

Only one grammar school, in Manchester, is thought to have been judged as failing before.

Head teacher David Marshall said he could not confirm or deny the contents of the report, but did say he was contesting its findings.

He said: “We received the report last Tuesday in draft form and had until [Tuesday this week] to identify any inaccuracies and that’s what we did.

“We sent to Ofsted seven pages of what we considered to be inaccuracies and the next stage after that is to see what the lead inspector comes back with and see if we’re going to put in any representations related to the conduct of the inspection.”

The final report, which could reach a different verdict, is not expected to be released until September.

A Medway Council spokesman declined to confirm or deny the contents of the report, and would not say whether the authority was offering help to the school.

Chatham Grammar for Boys is an academy, so it is independent but can accept council help if it is deemed to be struggling.

Last year the school was rated “satisfactory”. The category has since been replaced by one called “requires improvement”. This year, fewer than half of the school’s Year 7 places were filled in the first round of allocations.

That was despite 100% of pupils gaining five or more GCSEs at grades A* to C including English and maths last summer. At the time Mr Marshall blamed a population dip in Chatham.

Education adviser Peter Read said: “If [these reports are] true I would be very surprised because I talk to a lot of parents of students at the school and I have never heard a bad word about Chatham Grammar for Boys.”