A-level, AS and GCSE exams in Northern Ireland will start one week later in 2021 but will still finish by 30 June.
However schools have been told to keep evidence of pupils’ progress in case it is needed as part of contingency arrangements.
Education Minister Peter Weir has also decided on changes to what is taught in some subjects, mainly at GCSE.
This year’s exams were cancelled due to the coronavirus pandemic.
Instead calculated grades provided by schools were used to give results.
The government in Scotland has already decided to cancel National 5 exams - which are roughly equivalent to GCSEs - in 2021 and replace them with teacher assessments and coursework.
However in letters to schools and to pupils and parents about exams in 2021, Mr Weir said it was his priority to “ensure public examinations go ahead, if at all possible”.
“I believe that public examinations in these key qualifications are the most valid and reliable method of assessment available,” he wrote.
“The requirement to sit public examinations can provide a source of focus, motivation and engagement for many of our young people.”
But he said he had asked the Northern Ireland exams board CCEA to consider what he called “back-up” arrangements.
The minister said CCEA had been asked to tell schools an order that GCSE and A-level courses should be taught in.
“This means that in the event of further significant disruption due to the wider public health context, students have covered broadly similar content,” Mr Weir said.
“I would remind schools that it will be important that they retain a portfolio of evidence of pupils’ progression throughout the year in case this is needed at some stage for contingency arrangements.
“I am conscious that the public health situation is extremely fluid and that there may be further significant disruption as the year progresses.”
Exams will start a week later in 2021 - on 12 May 2021 - but will have to be completed by 30 June.
Mr Weir said that would allow for some more preparation and teaching time.
Pupils taking many GCSEs will sit fewer exams to take account of the fact that the majority of pupils were not in school from mid-March until the end of term in June and could still face further disruption to their studies.
In the majority of GCSEs, pupils will not be tested on one unit of their course.
In addition, the speaking element of GCSE modern languages qualifications and English language will not be assessed.
However, GCSEs in English language and maths will otherwise be unchanged.
“In taking this difficult decision, I have had to balance the merits of reducing the number of exams, with a need to protect the interests of our young people going forward,” Mr Weir said.
Most AS and A-level courses will see relatively few changes apart from to practical assessments and fieldwork in some subjects like geography.
Mr Weir has also decided that AS grades awarded in 2020 will still not count towards overall A-level results in 2021.
He said CCEA would be in contact with schools in the coming days to provide them with precise details of changes to individual subjects.
In England, a delay to the exam season of a few weeks has been proposed by the government.
That could affect some pupils in Northern Ireland who take exams through English and Welsh exams boards.