In the biggest shake-up of exams in a generation, traditional A* to G grades are being gradually replaced with a nine to one system.

Nine is the highest mark and seven is broadly equivalent to an A. Four is the new pass mark – equivalent to a ‘low C’. Five is a ‘high C’.

English and maths – key GCSEs for all teenagers – are the first to move over. Other subjects will follow over the next three years under the new system, driven by former education secretary Michael Gove.

The new number system reflects the new rigorous and traditional curriculum designed to stretch pupils and better identify academic high-flyers. The government believes it is the only way to compete with education powerhouses such as South Korea.

But it is feared nationally that only 2% of students will achieve the highest mark of grade nine in English literature. It increases marginally to 3% for maths. It follows warnings from school leaders that GCSE reforms are already causing teenagers more stress and anxiety.

The proportion of students gaining a grade four in English and maths is now the new benchmark, replacing the five good GCSEs measure.

Last night, some schools in the region issued results to this newspaper.

Hedingham School in north Essex achieved their best-ever GCSE results, according to headteacher John Panayi. Some 74% of pupils achieved at least a grade four in English and maths.

Mr Panayi said: “Within a changing and uncertain examination landscape where grade boundaries are untested, it is very good to note that Hedingham School has maintained high expectations.”

At Northgate High School, 71% of students achieved at least a grade four in English and maths.

Headteacher David Hutton said: “Despite changes making it impossible to compare some measures to previous years, the percentage achieving a C equivalent in both English and mathematics is up 3% at 71%.

“I would like to congratulate all pupils and staff on this fantastic accomplishment.”

Three-quarters of pupils also achieved at the new benchmark at another Ipswich school, this newspaper was told.

Former Suffolk secondary school teacher Sarah-Jane Page, director of Framlingham-based private tuition firm EASTuition, said the 9-1 grading system is as “clear as mud”.

She said: “Despite the apparent need to discern ability more plainly, lines now seem more blurred than ever. Where a ‘C’ once stood for ‘clear’ in terms of a pass, this year we’re told a four is a weak pass and a five a strong one.”

Former Suffolk headteacher Geoff Barton, the general secretary of the Association of School and College Leaders, warned “we are entering unchartered territory”.

He said: “Schools are going to see volatility in their results. Some will see some that are higher than expected and some will be lower than expected

“We have had exam reforms from Michael Gove which no-one really asked for. He explicitly said he wanted to make these exams more challenging. I think he could have done that by changing the existing GCSEs, but instead we have got a new mode of assessment and a new grading system.

“A lot of students who under the old system would have got an A* will get frustrated that they are now a grade seven or a grade eight.

“There is this increased anxiety among students… some will get a grade one, two or three and feel immensely frustrated that all the talk is about grade four and above.

“We don’t want to wrap up children in cotton wool… but in English Literature, not being allowed the text in front of you and having to memorise 19th century poems belongs to the 1950s. It was not something that parents and universities were crying out for.

“School leaders and teachers have done everything they can to make these hastily reforms work for students. We will have a post-mortem with the exam regulator to see what lessons can be learnt.”