Some schools are "over-testing" their pupils because they think exams will be cancelled, according to Education Minister Peter Weir.
He said some schools were putting "undue pressure" on pupils as a result.
The minister faced a number of questions about exams from MLAs in the assembly at Stormont on Tuesday.
Mr Weir also said the government in Wales, where summer 2021 exams have been cancelled, had produced a "David Copperfield solution."
"They have presented a few mirrors and made it look like exams have disappeared," he said.
He also said arrangements in Wales were "not particularly well sketched-out," and they were doing "exams under a different name."
Sinn Fein MLA Philip McGuigan had asked Mr Weir when he would provide contingency plans in the event of disruption to GCSE, AS and A-Level exams in 2021.
"I've indicated that exams will go ahead," Mr Weir replied.
"There has been a little bit of a - maybe sometimes genuine, sometimes false - discussion around 'when will you give certainty?'"
"Clearly, the certainty is that exams will take place."
"Some schools, concerned that exams will not take place, are over-testing their pupils on a daily basis."
"I think that's something that's entirely negative."
In 2020, as exams were cancelled, GCSE, AS and A-Level results were awarded using grades calculated by schools.
But Mr Weir warned that, if exams were abandoned in 2021, pupils would be put under "effectively a seven-month microscope, where every assignment, every action that they take would be a highly pressurised situation."
"Some of this is coming from schools who are taking a view that if they have to produce some level of evidence, for instance, as to what level of assessment they produce, they'll be worried about parents suing them etc," he said.
"This has then led to an undue level of pressure that's being place on a daily basis on children."
Mr Weir acknowledged some pupils had faced disruption but said CCEA had already reduced what had to be studied and exams in many GCSE subjects.
However, SDLP MLA Daniel McCrossan told the minister that: "most agree - students, teachers, parents - that the fairest option facing you and facing our young people is to cancel GCSE examinations this year."
But Mr Weir told Mr McCrossan and Green Party MLA Rachel Woods that exams were the fairest way forward.
"It's clear that examinations represent - however imperfect - the best opportunity for a level playing field between students," he said.
TUV MLA Jim Allister asked Mr Weir to confirm that primary schools would not close early for Christmas.
Mr Allister said that the last week before the Christmas holidays in primaries was "a particularly exciting and significant week."
He said that if schools closed early it would "bring devastation to many kids looking forward to those festivities."
Mr Weir replied that there was "no substance" to rumours of schools closing early.
"Schools will continue on in their normal Christmas period up until the week before Christmas," he said.
"Whenever the restrictions were talked about by the executive, the executive unanimously agreed - across all the parties - that schools should remain open."
"There are no plans to close schools early."