The "stacks" of tests sat by students in England and Wales should be cut to bring back balance to the curriculum, Britain's top exam official has said.
Too many exams could distort the system, Dr Boston warns
Qualifications and Curriculum Authority chief Executive Ken Boston said A-level exams could be reduced by a third within three years.
A* and A** grades could be introduced to help universities choose between top candidates, he told The Observer.
Too many exams could "distort" the education system, Dr Boston said.
He added: "The assessment load is huge. It is far greater than in other countries and not necessary for the purpose.
"We are pushing for the overall burden of assessment to be reduced."
Under QCA plans, the time spent by A-level candidates in exams would fall from 10.5 hours to a maximum of seven hours, the Observer reported.
Students would face four tests - rather than six - over two years to allow for longer, essay-style questions to distinguish the most talented.
Dr Boston said: "We need to look critically at the assessment regime.
"Assessment for learning is critical but stacks of (tests) can distort the balance of the curriculum and put too much emphasis on what is examined. I think this has been happening."
'Few more inches'
Tests had not become easier, but more students were gaining top grades, he said.
Dr Boston added: "We have got 22% cent of people at A-level getting an A. It may be time to add a few inches at the top."
More grades above A, such as A* and A**, and higher-level exams in science and languages at GCSE would help universities discriminate between students.
Teachers would also spend less time on the curriculum to allow for sport and culture lessons and special classes for the brightest, Dr Boston said.
A report on A-level maths published by the QCA last month said a "clever core" of students was dominating the subject.
While the number of students had fallen by 7,000 in five years, the number of A grades had risen by around 3,500, it found.
The QCA publishes its annual review on Wednesday.
Meanwhile, the government said it was "determined to ensure" that the brightest pupils were stretched.
A Department for Education and Skills spokesman said: "Our reforms include introducing tougher questions at A Level and catch up classes at Key Stage 3, measures that will support our wider aims of personalising education for each and every child."
He said the government was committed to raising standards in schools and added that testing was "here to stay".
The spokesman added: "Of course testing should not be over burdensome and for that reason the reforms we are making to secondary education will reduce the amount of coursework at GCSE and, where appropriate, A Levels will move from six assessment units to four."
Teachers broadly welcomed Mr Boston's comments, with union leaders saying that the exams boss was "absolutely right".
John Dunford, general secretary of the Association of School and College Leaders, said: "This is a good start to scaling down the bloated examination system in England, which is far greater than in any other country, and certainly more than is necessary to grade a student's achievement."
He said there was plenty of room for further reductions in testing at GCSE and A Level.
This could be achieved by making greater use of teachers' professional judgment of the standard of students' work over the two years of the course, Mr Dunford added.
Steve Sinnott, general secretary of the National Union of Teachers, said: "Ken Boston is absolutely right. We have an absurd exam workload, both for children and teachers.
"I think it's a breath of fresh air, a clarion call to the Government to say the tail is wagging the dog, testing is dictating what's taught, and it's dominating the life of schools."