A move to cut A-level re-sits would be a "step in the right direction", a group of leading universities said on Tuesday.
Students should be given a second chance at an exam, but should not be allowed to re-take a paper frequently, The Russell Group suggested.
But it also indicated that an attempt to scrap AS-levels completely could be a set too far, as the qualifications are useful to universities.
The comments come as Ofqual, the exams regulator, prepares to publish its proposals for A-level reform.
The document, due to be published later today, is expected to set out plans for a major overhaul of the system in a bid to boost standards.
It is likely to call for a limit on the number of times that a student can sit a paper and may propose axing the January exam session.
Under the current system, exams can be taken in January and June.
The proposals, which are being published for consultation, are also expected to contain plans for universities to have a greater involvement in setting A-levels.
There have also been suggestions of a move towards scrapping AS-levels entirely.
Dr Wendy Piatt, director general of the Russell Group, which represents leading universities including Oxford and Cambridge, said: "While A-levels are broadly fit for purpose, we do have several concerns. With the current modular system, students too often quickly forget the 'bite-sized chunks' of knowledge they have learnt.
"This makes it harder for them to have an overall grasp of that subject, to synthesise information and to become independent learners. This consultation's proposals on ending the modular system and January exams are welcome.
"The proposed reduction in the number of re-sits that students are allowed to do would be a step in the right direction.
"We think it's fair that people are given a second chance if they have good reasons for under-performing in an exam, but more recently students have been allowed to do re-sits too frequently.
"Our universities are concerned that many of the students who don't get the grades first or second time around don't go on to do as well in their chosen degree course.
"AS-levels are useful to universities - as indicators of post-GCSE progress - and to students seeking to develop a broader range of knowledge."
She added that the AS exams and the so-called A2 exams taken in the second year of A-level study should not necessarily be given equal weighting.
"We have some concerns about the content as well as the structure of A-levels," Piatt added.
"Maths A-level poses particular problems: some modules are just not challenging enough to equip students not only to do a maths degree but also to go on to to degrees in engineering or physics.
"There has been too much focus on an 'emotional' response to texts rather than on robust critical analysis in some subjects like English."
Last year, more than 250,000 teenagers in England, Wales and Northern Ireland took A-levels.
One in 12 exams achieved an A* grade while more than one in four (27%) exams achieved at least an A.
Anthony Seldon, headteacher at Wellington College, said:
"The proposed changes to A levels are a step in the right direction, in that it would be a move away from the mindless ‘satnav’ A level towards a real test of the student’s abilities and the exams would be much more likely to inspire challenging and thoughtful teaching. However, they are still some way short of the rigour, the breadth and the depth of the International Baccalaureate."
In April, Education Secretary Michael Gove announced that he intends to give universities, particularly the most elite institutions, "a far greater role" in designing A-levels in the future amid concerns that the qualifications are failing to prepare teenagers for degree study.
In a letter to Ofqual, Gove said he did not envisage the Government playing a part in developing A-levels in the future.
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