An independent committee on exam standards said that it was difficult to see how more care could be taken to ensure that grades were accurate.
The committee, set up after the 2002 A-level regrading fiasco, said it was impossible to say whether exam standards had risen or fallen in recent years, or whether some subjects were harder than others. It made little sense to ask whether standards have been maintained over a long period of time because of syllabus changes.
Barry McGaw, who chaired the inquiry, said: "The English examination system... is not faultless, but we know of no better examination system."
The three-person inquiry, led by Dr McGaw, director for education at the Paris-based Organisation for Economic Co-operation and Development, looked at how standards were monitored.
The Qualifications and Curriculum Authority has been comparing standards from year to year in around six subjects since 1997.
But there were problems: syllabus and exam papers could change significantly; it was difficult for experts to avoid making subjective judgements; and evidence, including mark schemes, dating from before the late-1990s, was often unavailable.
The QCA set up a national archive of exam papers, scripts and supporting materials in 1997, but it was still difficult to come to anything other than tentative conclusions, because of changes to subject courses. For example, in history, exams had changed in the past 20 years from emphasising knowledge to requiring evidence of students' interpretative and evaluative skills.
The report said: "Over the longer term, it makes little sense in many subjects to ask whether examination standards have been maintained since the subjects themselves have changed so much."
It would be helpful, it said, if the public asked not whether standards were falling but whether exams were making reasonable demands of students.
However, Ruth Lea, director of the Centre for Policy Studies, the right-wing think tank, said universities' complaints that 18-year-olds'
knowledge in maths, science and languages was falling meant it was obvious standards were declining.
No exam system had found an adequate way of determining whether it was easier for students to achieve high grades in certain subjects than others, the 40-page report added.
It said checks in England's exam system ranged from lengthy discussions between examiners on grade boundaries to markers being graded for their work.
It praised the QCA for becoming more communicative with the public about exams, but said only limited progress had been made in addressing previous recommendations for more research.
NEWS 16 ANALYSIS 22