Professor Gordon Stobart from University College London suggested that exams were not the most effective way to assess pupils who would leave school at 16 and expressed concern about the "sheer volume" of tests in Scottish schools.
Prof Stobart, who wrote a report for the Organisation for Economic Co-operation and Development (OECD) about assessments in Scotland's Curriculum for Excellence, said he was shocked by the complex Scottish system.
His report compared Scotland's system with those in nine other places worldwide, including England, Wales, Ireland, Hong Kong, New Zealand and Norway and concluded it "loses strength" in the senior years as there can be a focus on "teaching to the test".
Giving evidence to MSPs, Prof Stobart indicated he was in favour of exams for pupils aiming to go to university but suggested the reforms for pupils aged 15 and 16.
"I think probably the biggest surprise was the sheer volume of examinations that secondary school students go through, the complexity of National 5, the Highers and the Advanced Highers, and that you may have multi-level teaching in small schools with students going in for different ones where there's slightly different curricula," he said.
Prof Stobart added: "I think we can record progress and we don't necessarily need a national examination to do it - there may be other ways.
"I talk about a mixed economy in which we need examinations and I think, certainly for university, I've not attempted to say that we don't need [them for] the Highers and the Advanced Highers.
"It's more at the National 5, whether there are other ways of recording progress and recording what students have done with their school experience."
Prof Stobart cited the International Baccalaureate and said: "You could say it it's an assessment and it's got exams in it, but it's also got other aspects, the essay, the theory of knowledge, the personal projects.
"These kinds of things can be built into it so it doesn't need to be a narrow preparation for exams which I suspect can become quite didactic at times - 'you're here to learn this, this and this' - rather than engaging with students on developing ideas, their profile and community service which in Canada is part of the International Baccalaureate."
Asked about potentially reforming the school leaving age, he suggested the Scottish school system was doing this "almost naturally" already, with 88% of pupils now staying in education beyond the age of 16.
"That's up dramatically from 20 years ago when most students did leave at 16 - and that was the justification for examinations at 16 as well."
He added: "Early leavers often have very little to show in terms of exam results and the like.
"That would be my experience and my reading of the Scottish statistics on this.
"Perhaps my suggestion of some kind of portfolio, some kind of graduation thing, could take into account far more and give a richer picture - even if they're leaving - of what they did in school, what were their strengths?
"I would not see leaving exams that students are often unsuccessful in as a good way to end their formal education."
Last month, Scotland's Education Secretary, Shirley-Anne Somerville, said exams could be reformed but not scrapped.
She announced work to possibly reform exams is due to start in the new year and said: "The issue of assessment and qualifications generates strong and sometimes conflicting opinions.
"However, I am convinced that, given the experience and views expressed over the last two years, the time is right to signal that the Scottish Government supports reform of national qualifications and assessment."
Ms Somervillle added: "We're not talking about ending exams.
"What we are talking about is having a discussion about the best way of us being able to look at what a learner achieves and recognise that achievement."