Up to one-in-13 examinations taken in England, Wales and Northern Ireland is set to be an A* - twice the number when the grade was first awarded in the mid-90s.
But education experts said that pupils with a string of top passes were “left bored”” by the qualifications because of a sharp rise in the number of tests they are forced to sit.
Most GCSEs are now broken down into a series of bite-sized units with an exam at the end of each one.
Nansi Ellis, head of education policy at the Association of Teachers and Lecturers, said the exam-focused nature of the system meant children accummulated test results instead of developing their skills.
"Even those who achieve a string of A*s are not well served by GCSEs; they are taught to pass tests, rather than encouraged to learn skills and leave bored by endless testing," she said.
"And crucially our exam-obsessed system is not designed to develop the softer skills, such as creativity, initiative, problem-solving, reasoning, and team-working, that young people need for higher education, work and their future lives.
"The Government desperately needs to end its obsession with exams and agree an assessment system that meets the needs of today's young people."
Some 750,000 teenagers will receive the results of GCSEs and other vocational courses on Tuesday.
Prof Alan Smithers, director of the Centre for Education and Employment Research at Buckingham University, predicted that around 7.5 per cent of entries would be awarded an A* this summer, while more than 22 per cent will get an A* or an A.
He said year-on-year rises were being driven by the “structured” nature of questions.
“The teachers know now what the exam boards are looking for in answers,” he said. “It's the importance of the results to the schools.
“The questions themselves are becoming much more predictable; they are highly structured and teachers are increasingly familiar with them.
“It is true that league tables make it very important for schools to make sure that their children get good scores but there is also a sense in the examiners themselves feel they are doing a good job if the scores nudge up a bit each year.
“Exams just seem to have the same built-in inflation that our currency has. Although they will deny it, examiners seem quite happy if there is a little bit of inflation each year.”
--By Graeme Paton, 23 Aug 2010