The GCSE exam system in England faces a shake-up which will mean a single end-of-course exam, fewer top grades and one exam board for each subject.
Education Secretary Michael Gove and Deputy Prime Minister Nick Clegg will confirm the plans for reform.
Pupils who have begun secondary school this year will be the first to take the revised exams in 2017.
Mr Clegg promised that the changes would "give parents confidence" in the exams taken by their children.
But Labour's shadow education secretary, Stephen Twigg, attacked the plans as "totally out of date, from a Tory-led government totally out of touch with modern Britain".
"Schools do need to change as all children stay on in education to 18 and we face up to the challenges of the 21st Century. We won't achieve that with a return to the 1980s," said Mr Twigg.
Single exam board
Details of the changes to GCSEs in England will be formally announced to MPs on Monday afternoon.
But a series of leaks have suggested that the shake-up will mean that the current system of assessing individual units of a course will be replaced by a single three-hour final exam.
The first pupils would begin studying these exams in 2015 - with the first candidates taking the new-look exams in 2017.
There is also likely to be one exam board for each subject - rather than having different exam boards competing with their own versions.
There have been claims that such competition leads to a "race to the bottom", with an incentive for exam boards to attract more business by making it easier to pass.
It is also expected to be made more difficult to get the highest grades - with the suggestion that the A* and A grades will be replaced with a top level that fewer children will be able to achieve.
A leak during the exam season had claimed that GCSEs would be abolished and replaced with an O-level for the more able and a separate exam for pupils of a lower ability.
But this prompted a dispute within the coalition over introducing such a two-tier system - which seems to have been resolved to create a single exam for all ability levels.
Addressing the education select committee last week, Mr Gove suggested that an exam could be taken at different points between 16 and 18 years of age - allowing weaker pupils to catch up.
The changes to the GCSE exam will come alongside the raising of the leaving age - which will see young people staying in education and training until the age of 18.
Mr Clegg said the changes would "raise standards for all our children", but he added that it would "not exclude any children".
He said it would have been wrong to go back the old dual exam system - and set out what he hoped would be gained from the revised GCSEs.
"Firstly give parents confidence in the exams their children are taking, secondly raise standards for all our children in schools in the country but thirdly and crucially not exclude any children from the new exam system."
When more details of the new exam were leaked at the weekend, Labour said it supported more rigorous exams but only if they do not act as a cap on aspiration.
A reform of the exam system in England will not apply to pupils taking GCSEs in Wales - and this shake-up could see a greater divide between qualifications in England and Wales.
The Welsh government says it will not be rushed into following any changes to the GCSE and is carrying out its own separate review into the exam system.
Changes to the GCSE in England would not apply to Northern Ireland.
Former chief inspector of schools Sir Mike Tomlinson - who conducted a review of the exam system for the previous government - told BBC Radio 4's Today programme he thought the planned change was "largely positive".
He backed the move away from a modular system and plans for there to be only one board to examine in English, mathematics or the sciences.
Back to the future?
But he questioned how subjects that do not lend themselves to a single exam, such as art and dance, would be tested in a single exam.
Brian Lightman, general secretary of the Association of School and College Leaders, said GCSEs needed to be reviewed but bringing back an O-level style exam was not the answer.
"I hope that these proposals are not going to be telling us that we're going to have a system that goes back to something that we used to have in the 1950s, which was suited to a very small part of the population," he said.
Martin Johnson of the ATL teachers' union said: "A new exam certainly should not be designed on the back of a restaurant menu as a short-term political fix by ignorant ministers. This is an insult to the nation's children who will have to live with the consequences if the crackpot ideas are implemented."
"Tinkering with exams is a cheap and relatively easy lever for governments, which has been used and over-used in the past couple of decades. What would make a real, long-term difference to raising standards for all children would be improving the teaching and learning in all schools - but that's long, and hard, and expensive," said Kevin Stannard of the Girls' Day School Trust.
The plan to reform the exam system comes amid controversy over this year's GCSE English exams - with head teachers claiming that grade boundaries have been unfairly altered.
The exam regulator in England has refused to regrade the disputed papers - but the Welsh government has instructed the WJEC examining board to carry out a regrading in Wales.
In Scotland, pupils take Standard Grades, Highers and Advanced Highers rather than GCSEs and A-levels.