Exams motivate children, giving them a sense of satisfaction and happiness, Michael Gove is to say.
The Education Secretary is to argue for rigorous testing at the Independent Academies Association's conference in North London.
He is expected to say easy exams are even worse than no exams as they fail to motivate pupils and support those who need it.
He is also expected to defend school league tables, suggesting that they have helped to overcome prejudice against schools in disadvantaged areas.
Mr Gove will tell the conference "exams matter because motivation matters".
He says: "If we know tests are rigorous, and they require application to pass, then the experience of clearing a hurdle we once considered too high spurs us on to further endeavours and deeper learning."
Mr Gove says that American cognitive scientist Daniel T Willingham has suggested that students are motivated to learn if they enjoy "the pleasurable rush that comes from successful thought".
"We know that happiness comes from earned success," the minister says.
"There is no feeling of satisfaction as deep, or sustained, as knowing we have succeeded through hard work at a task which is the upper end, or just beyond, our normal or expected level of competence."
Mr Gove will also say: "Exams show those who have not mastered certain skills or absorbed specific knowledge what more they need to practice and which areas they need to work on.
"For all these reasons exams pitched at a level which all can easily pass are worse than no exams at all. Unless there is stretch in the specification, and application is required to succeed, there will be no motivation, no satisfaction and no support for those who need it."
He suggests that exams are a "guarantee of competence" and that it is vital for children to learn facts, and commit them to memory.
Testing requires pupils to show they have "absorbed and retained knowledge", he adds, and means that teachers are forced to develop ways of holding pupils' attention.
Issuing a staunch defence of externally-marked tests and league tables, Mr Gove will tell the IAA that "over the last few years, tests have helped overcome prejudice and advance equality."
He adds: "Proper tests, that is. Externally set. Externally marked. With results recorded in league tables."
Mr Gove says that while he is a "huge fan" of teachers marking tests, external exams are "fairer".
"The evidence shows that in teacher assessment of English achievement there is a tendency for ethnic minority children to be under-marked and students from non-minority backgrounds to be more generously marked.
"With external testing there is no opportunity for such bias - the soft bigotry of low expectations - and tests show ethnic minority students performing better. So external tests are not only a way of levelling the playing field for children of all backgrounds, they are a solvent of prejudice."
He adds: "In the past, before the clarifying honesty of league tables, schools were judged on hearsay and prejudice.
Schools with challenging intakes in disadvantaged communities were written off as sink schools. But many of them were performing well - better than other schools with more privileged intakes which were coasting. But their success - particularly at primary level - could not be effectively established."
League tables have shown that there are many primaries in disadvantaged areas that are outperforming other schools, he says.
"Testing has overcome prejudice."
These tables also help to identify high-performing schools and pass on the reasons for their success, as well as those that are failing.
Mr Gove's speech comes just weeks after an Ofqual report into problems with this year's GCSE English exam laid blame on intense pressure on schools to reach certain targets, which led to over-marking by teachers.
Under the current system, schools are judged on the number of pupils who score at least five C grades at GCSE, including English and maths.
This measure is included in league tables, with schools expected to have at least 40% of students reaching this standard.
Those which do not, and fall short on other pupil progress measures, are considered failing.
Ministers have already announced plans to scrap GCSEs due to concerns of grade inflation and "dumbing down" of the exams.
Plans to reform A-levels are also being considered.