Education Secretary Michael Gove has confirmed major changes to A-levels in England but the plans have had an unenthusiastic reception from head teachers and university leaders.
From 2015 pupils will take exams at the end of two-year courses.
AS-levels will remain, but as stand-alone exams, and a group of leading universities will play a bigger role in maintaining standards.
Independent school head teachers attacked the proposals as "incoherent".
Brian Lightman of the Association of School and College Leaders said: "This is a classic case of fixing something that isn't broken."
The organisation representing leading private schools, the Headmasters' and Headmistresses' Conference, called the proposals "rushed and incoherent" and said they were driven by a "timetable based on electoral politics rather than principles of sound implementation".
The University of Cambridge has also voiced strong criticism of the changes to AS-levels, issuing a statement saying it will "jeopardise over a decade's progress towards fairer access to the University of Cambridge".
In a letter to exam regulator Ofqual, Mr Gove said A-levels in their current form did not help students to develop a "deep understanding" of their subjects.
Instead modular units will be scrapped, with the qualification returning to exams taken at the end of a two-year course.
This shift away from so much piecemeal testing was welcomed by the Girls' Day School Trust.
"The educational advantages of linearity and of learning within a coherent continuous two year course are clear, and will be seized on by schools like ours that seek to put teaching above testing," said the trust's Kevin Stannard.
The AS-level exam will remain, but will no longer be taken after a year or count towards a full A-level. It will instead become a stand-alone qualification, taken alongside full A-levels after two years in the sixth form.
Many universities currently offer places using students' AS-level results. Nicola Dandridge of the higher education body, Universities UK, said the change would mean universities having to place more emphasis on other evidence such as school references which might disadvantage some pupils.
The AQA exam board said that it was "disappointed" that AS-levels would no longer be part of the wider A-level.
There will be a bigger role for leading Russell Group universities in supervising the content, although this might take the form of organising committees of specialists, rather than taking direct responsibility.
The introduction of an A-level Baccalaureate, closer to the International Baccalaureate, which was discussed last year does not appear as part of this package.
The A-level changes call for the end of assessing "modular" chunks of learning, and a return to a "linear" form, with exams at the end of the course - but Ofqual says this will not necessarily mean an end to coursework in A-levels.
Schools Minister Liz Truss said the plans would end a system where students are preparing for exams almost as soon as they begin a course.
"Pupils spend too much time thinking about exams and re-sits of exams that encourage a 'learn and forget' approach to studying," the minister said.
Stephen Twigg, Labour's shadow education secretary, rejected the argument behind the changes, and warned that it would narrow options for young people.
"It's no wonder leading universities like Oxford and Cambridge say this is a mistake. We need to have more high quality options available at age 16, including all young people studying English and maths to 18."
Teachers' unions say the changes to A-levels are being taken forward in a "cavalier" fashion without adequate evidence.
Chris Keates of the teachers' union NASUWT, said: "Rather than recycling the incoherent grumblings of a few isolated and unrepresentative academics, the secretary of state should take note of the fact that there has been no clamour for reform.
"Employers have not identified A-levels as problematic," she said.
The Association of School and College Leaders (ASCL) said the decision flew in the face of overwhelming feedback from a recent consultation that found that the "current system needs tweaking but is broadly fit for purpose".
"It is disappointing that this has ignored the overwhelming views of the teaching profession, academics, employers and universities to retain the link between AS and A level," said general secretary, Brian Lightman.
Neil Carberry, the CBI's director of employment and skills said: "Businesses want more rigorous exams but we're concerned that these changes aren't being linked up with other reforms, especially to GCSEs. We need a more coherent overall system."
Pam Tatlow of the Million+ university think tank said "These proposals risk creating a two-tier A-level system which will complicate university admissions and reduce opportunities for students."
Students in Scotland have a different exam system while the devolved governments in Wales and Northern Ireland will make their own decisions about whether to implement the changes to A-levels.