Scottish exam chiefs say disqualifying pupils caught with mobile phones is a matter of fairness to all candidates.
Pupils were warned to hand over phones ahead of exams
More than 100 pupils will be failed in Higher and Standard Grade papers because they took phones into their exam halls.
The Scottish Qualification Authority (SQA) insists pupils were warned that anyone caught would be disqualified, even if there was no proof of cheating.
Scotland's exam results are due out on 9 August.
The SQA has had 109 allegations of mobile phone abuse referred to it by schools, most of which were not direct attempts at cheating.
But Mike Haggerty, the authority's director of communications, told BBC Radio's Good Morning Scotland programme a tough stance had to be taken.
He said: "Our invigilators stand up and make an announcement asking candidates to hand their mobile phones in if they still have them on them.
"It quite clearly states that mobile phones should not be in the exam room, that's black and white.
"Our difficulty here is phones that have gone off and disrupted the many thousands of others who have stuck by the rules.
"Virtually in all cases it is going to dictate what happens for the rest of people's lives and that's why we have to make sure that we take care of fair and honest conditions for the majority of candidates."
Judith Gillespie, of the Scottish Parent Teacher Council, said there was no point in having a rule if it was not enforced.
Scottish Secondary Teachers' Association general secretary David Eaglesham also backed the sanctions.
Mr Eaglesham said: "This is the electronic version of when people used to hide little folded up bits of paper behind their ears in the dim and distant past."
The SQA also revealed that a further 41 Higher and Standard Grade school pupils had been failed for plagiarising the work of other students and authors.
More than 500 different exams were sat by 145,000 Scottish pupils during this year's six-week exam period.