Every school has now submitted results to Suffolk County Council (SCC), which has confirmed that 64% of students scored at least a grade 4 in both key subjects this year.
Although experts say results cannot be compared to previous years due to the reforms, it is a three-point percentage annual rise.
The figure was first reported as 63% after only 80% of schools issued data on results day.
Graham White, of the Suffolk NUT, said: “Many pupils have particular needs which may mean they perform less well in exams, which is why coursework and oral components are so important. These have been largely removed as a result of government changes. We are moving towards, or backwards, into 1950s-style exams of rote learning and factual recall rather than deeper understanding and critical thinking.
“But it is very encouraging that pupils in Suffolk have done well. This is the first year of the new exam system so we should not analyse too deeply about which schools have done the best.
“However, all schools should be congratulated on the efforts made by pupils, teachers, support staff, parents and governors in an attempt to do the best they could.
“The intake, relative poverty and social area are the single biggest factors in determining pupil outcomes so the school results overall are not a surprise.”
Schools minister Nick Gibb said pupil and teachers are “rising to the challenge” of the new GCSEs.
Ofqual chief regulator Sally Collier said: “(The) results reflect years of careful planning.
“We have used the same tried and tested principle of comparable outcomes, as in previous years, to ensure that this first cohort of students is not disadvantaged.
“If a student receives a grade 7 today, they could have expected to have received a grade A last year.
“And if they get a grade 4, they could have expected to get a grade C in 2016.”
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