The number of youngsters caught cheating in GCSE and A-level exams rose by 27 per cent last summer.
More than 1,000 pupils - one in four of those caught - were disqualified for using mobile phones in the exam hall, according to the Qualifications and Curriculum Authority, the Government's exams watchdog, in a report published today.
Some were caught texting friends outside the examination hall - seeking answers to questions.
The use of mobile phones in examinations has soared in the past few years - and is now the biggest single cause of malpractice.
In all, 4,547 youngsters were found guilty of cheating last summer - compared with 3,573 that were caught the previous year.
The figures have prompted Dr Ken Boston, the chief executive of the QCA, to write to all schools urging them to stress to pupils the importance of not taking mobile phones into examination halls.
"Over recent years, we have seen a noticeable rise in the number of mobile-phone-related incidents in examination halls across the country," he said. "There are clear and serious penalties for students who cheat in their examinations. Anybody who cheats in their exam will be disqualified and will lose their grade in that subject."
A breakdown of the cases of pupils cheating reveals 520 proven cases of plagiarism - mostly students ripping off answers to coursework from the internet.
There were 410 cases of collusion in the examination room and 300 of disruptive behaviour during the exam.
"Overall," said the report, "about one-third of penalised candidates were involved in plagiarism, collusion or copying another candidate's work."
In nine cases, pupils were caught impersonating the person who should have been sitting the exam. And in seven cases, one student's work was stolen by another.
A spokesman for the Department for Education and Skills said: "We expect schools to maintain high standards of discipline.
"We have been very clear - there is no place for mobile phones in the classroom let alone in the examination hall."
Today's report also reveals that more than 17,000 pupils had their grades changed as a result of calling for a marking review - 5,641 at A-level and 11,683 at GCSE.
However, it makes it clear this is less than 1 per cent of all scripts submitted.
It reveals that 40 question papers last summer revealed errors in the way the questions were framed - thus making it almost impossible for candidates to answer them. However, this is a drop from 2.4 per cent of all papers to 1.2per cent compared with the previous year.
Caught in the act
1,887 cases: Introducing unauthorised material into an examination room
484: Copying from other candidates
435: Obtaining, receiving or passing on information
300 Disruptive behaviour (including offensive language)
208 Inappropriate, offensive or obscene material in exam answer
133: Failure to follow instructions
94: Failure to follow awarding body supervision requirements
32: Behaviour undermining integrity of exam
13: Altering documents - including certificates
10: Destruction of work
9: Personation, i.e pretending to be someone else
7: Theft (of another candidate's work)
5: Misusing materialReuse content