For generations, hundreds of thousands of pupils have spent the end of the school year in gymnasiums scrawling answers to the sound of the ticking clock. And every summer they have endured a nerve-wracking two-month wait for their results.

Exams have been a rite of passage for millions, but within a decade they could be consigned to history, according to one of the most senior figures in the system.

Simon Lebus, chief executive of Cambridge Assessment, said that traditional examinations are likely to disappear within 10 to 15 years, to be replaced by computerised testing.

Instead of three-hour written exams, there will be continual e-assessment throughout pupils' courses. Exam boards are investing millions of pounds in developing the technology – and, Lebus claimed, it's not "science fiction".

He said: "The likelihood is that in the next 10 to 15 years it will change almost out of recognition in that by the end of that period of time you'll be able to do exams more or less on demand, on screen.

"You can make the learning more valid and the technology can enhance the way people engage in the subject. It's very expensive, complex stuff to do. But it is achievable. It's not a vision based on a sort of science-fiction type fantasy."

Lebus, a former investment banker, has since 2002 headed Cambridge Assessment – a department of Cambridge University and the umbrella organisation for international exam boards including OCR, one of the three operating in England.

He said that traditional-style exams would still be available for those who preferred them, but the new system would benefit students who are exam-phobic. "There are some people obviously who get very frightened by exams or couldn't for other reasons do them well. They would be well suited to an environment where there were no exams."

Originally A-levels were assessed in one set of exams at the end of a two-year course. Nine years ago Curriculum 2000 was introduced, when pupils were allowed to "cash in" their courses as AS levels at the end of the first year. In September GCSEs will follow this model, with pupils allowed to retake courses to improve their marks.

The computerised world that Lebus envisions would go further down that route, allowing pupils to take tests when they are ready. As they complete tasks online their progress would be monitored and tracked without them having to take tests. It could involve "adaptive" testing, which would generate harder questions when a pupil gets an answer right or easier ones when they are wrong. Such tests are thought to be more accurate at diagnosing a pupil's level of skill.

OCR has piloted a fully e-assessed GCSE in environmental and land-based science since 2007. This summer 1,800 candidates at 80 schools and colleges will take it.

The moves are part of a global shift towards computerised assessments. The US is leading the way with multiple choice and computer marking, while South Korea is rapidly developing new e-assessment models. Denmark is piloting the use of the internet during some essay-based exams, seen as the equivalent of the move to allow calculators in maths exams.

Some academics warn against the shift. Alan Smithers, professor of education at Buckingham University, said: "Making judgments about performance isn't easy. The best way of doing it is dispassionate assessment of students tackling the same tasks under the same conditions."

Dylan Wiliam, a leading exam expert at the Institute of Education, University of London, said: "There is no doubt that you could have a completely wired-up classroom where every keystroke will count towards an assessment. But that is too horrible to contemplate, the idea that students are under pressure all the time. We need a culture where kids can make mistakes without being penalised."

But John Dunford, general secretary of the Association of School and College Leaders, said: "Too many people believe that the only legitimate examinations are the ones they took at school many years earlier. The world moves on and assessment should move on too."