More Norfolk pupils received top A-level results following changes to this summer's grading system, but still fell further behind other parts of England.
Exams were cancelled amid the coronavirus pandemic and, following a U-turn, students were given a choice of their predicted grades or ones calculated by an algorithm.
Educational charity The Sutton Trust, which champions social mobility, said regional inequalities seen in the marks suggests that pupils may have been disadvantaged by their postcode.
Department for Education (DfE) figures show 3,119 students in Norfolk took A-levels in 2019-20 – with 18pc receiving three A* or A grades, 28pc AAB or better and 83pc at least two A-levels.
The proportion getting A*-As was much higher than the eight per cent of pupils who achieved the same result under normal circumstances the year before, but the gap to the best performing parts of England has grown.
In 2018-19, Norfolk was 22 percentage points behind best performing area Reading, but this grew to 28 this summer.
Meanwhile 28pc of Norfolk children achieved grades of AAB or better in the most recent academic year – up from 15pc the year before.
But the gap to Reading, which was again the top area in this measure, grew from 24 to 29 percentage points.
James Turner, chief executive of The Sutton Trust, said: "It is troubling to see a big increase in the regional divide for top grades, suggesting that pupils may have been disadvantaged by their postcode.
“It is imperative we avoid a similar situation this year. Contingency plans should be in place if exams can’t go ahead in the summer, including ongoing assessment through coursework, or benchmarked assessments set by exam boards in the place of mock exams, which are too inconsistent to be reliable.”
Geoff Barton, former Bury St Edmunds head and general secretary of the ASCL, which represents most secondary school heads, said “business as usual” with next year’s exams was “not sustainable”.
“We can’t possibly send in young people to do exams and answer questions on topics they may not have covered, it just would not be right,” he said.
A DfE spokesman said: “Exams are important in judging a pupil’s performance and this data reflects the unprecedented circumstances faced this year. That is why Ofqual and the Government agree that exams should go ahead next year.
“Exams give all pupils the best possible opportunity to demonstrate their ability and achieve the results they deserve, no matter what their background."
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