England's school qualifications system is helping to perpetuate socio-economic divisions in the take-up of university places, researchers are warning.
Children from poorer backgrounds choose vocational qualifications not valued by higher education, research by Ucas, the universities admissions service, reveals.
Some of these courses, such as the popular OCR nationals, the exam-free alternatives to GCSEs and A-levels, barely register in entry requirements for university, so students might find they are of little use in aiming for higher education.
This means that the chances of going to university are being heavily influenced by course choices at 14. But pupils appear not to be being made aware of this at school.
The findings were presented to a seminar run by the Oxford University- based Nuffield Review of 14-19 qualifications. The admissions service ran a check on the information on university websites about entry requirements. Some 93 per cent gave information about A-levels, such as which one pupils needed to take and what grades were required. The only courses that failed to provide this were those where A-levels were not relevant, such as postgraduate study, said Ucas.
Some 81 per cent included information on advanced vocational A-levels; 55 per cent on Btec national diplomas; and 21 per cent on OCR national diplomas. This is despite qualifications such as the OCR nationals being given high weighting by Ucas's tariff system, which suggests they should be seen as at least as valuable as A-levels.
Harriet Dunbar-Goddet, a Ucas research officer who presented the paper, said this meant that some vocational qualifications were "invisible" in the eyes of admissions tutors.
"For all courses and types of institutions," she said, "A-level applicants had detailed information and were not asked to combine qualifications with a vocational one. Many courses had no detailed information for vocational applicants, and instead they were told to contact the institution."
It could be difficult for a student having to contact a university and explain a course to an admissions tutor, Dr Dunbar-Goddet said. By contrast, many university courses requested that a vocational qualification be taken in combination with an A-level.
Separate data showed clear class differences in the take-up of school exams. The international baccalaureate draws 70 per cent of its candidates from what statisticians count as "higher socio-economic groups", such as managers and professionals, Ucas found. The comparable figure for A-levels was 59 per cent. For vocational courses, which were lumped together in one category by Ucas, the figure was 41 per cent.
Ucas is concerned that qualifications are dividing students by class at the age of 14, sending disadvantaged pupils down a track which is unlikely to lead to a prestigious course in higher education.
"Students are being pushed in certain directions in qualifications," Dr Dunbar-Goddet said. "It seems as if the students are getting information about certain qualifications they can take and then, once they have taken these qualifications, might find some avenues are no longer open to them."
There was some questioning of the research at the seminar. One participant suggested that it was wrong to include all vocational courses together in the analysis of qualifications by social class.
However, a separate study in 2005 for the Nuffield Review confirmed that some admissions tutors were ill-disposed to vocational courses and knew little about them.
Some observers say that the increasing diversity of school qualifications - the international baccalaureate, the Cambridge pre-U and the new 14-19 diplomas all competing with A-levels - will lead to a hierarchy of exams. They believe pupils at private and grammar schools will take the international baccalaureate and the pre-U, while working class pupils take diplomas.
John Bangs, the National Union of Teachers' head of education, said: "We are moving into a situation in which the qualification you take may broadly match your social class. It's worrying." He said it was shocking that admissions tutors had such attitudes to vocational courses.