Pupils are choosing their A-levels according to how easy they think subjects are, a poll of teachers has found.
More than a quarter (26 per cent) of teachers believed their students' perceptions about the difficulty of different A-levels influenced their choice of exams to "a great extent" and another 59 per cent "to some extent".
The findings from a representative sample of more than 900 state secondary teachers will fuel fears that maintained school pupils are missing out on top university places by opting for "soft" subjects.
Professor Alan Smithers from Buckingham University said: "Some comprehensive schools will be seeking to have a wide range of subjects to attract young people to stay on.
"For pupils who have not done very well at physics or French, they might say: 'You could do film'. That is fine, but young people need to be aware that the traditional subjects are the main ways we make sense of the world and are the sort of subjects universities are looking for."
In June, it was revealed that 10 per cent of comprehensive pupils took a media studies A-level, identified as "soft" by the elite Russell Group of universities, compared to just 1.5 per cent of private-school pupils.
Conservative MP Elizabeth Truss, who obtained the figures, said they showed schools had "mis-sold" pupils "low-quality subjects".
The latest poll, conducted by the National Foundation for Educational Research (NFER) for exam board AQA, shows that almost two-thirds (65 per cent) of teachers agree that pupils who receive "high-quality" careers advice are more likely to consider taking subjects perceived as difficult.
The finding comes a week after a panel of Government advisers warned that the "foolhardy" "destruction" of the country's careers service risked damaging young people's lives and the economy.
AQA noted that the NFER poll showed that most students were advised by subject teachers, but that there was a need for impartial advice.
The exam board's own Centre for Education Research and Policy separately studied around 500 pupils making A-level choices.
It found that perceptions of ease or difficulty were not a factor when considering media studies but did play a part for physics.
Expectations of parents and teachers were the "most important factor" in their choices, it said.
Michelle Meadows, head of the centre, said: "While we found that students' A-level choices are influenced by perceptions of difficulty, other beliefs are more important. In particular, students are more likely to choose subjects like physics, if they believe that teachers, parents and friends will approve of and support their choice."
Association of School and College Leaders general secretary Brian Lightman said: "There is a deterrent to students choosing a subject that they know will be more difficult. But people are becoming increasingly aware of the value of certain subjects - last year we saw an increase in STEM subjects."
"Patchy" schools' careers provision is hindering efforts to significantly raise pupil interest in science, technology, engineering and maths (STEM), Government-commissioned research has found.
The National Foundation for Educational Research report found that heads and deputies did not always prioritise STEM careers information and guidance. There was "patchy careers provision in schools alongside a small careers workforce", it said.
The research suggested that including careers in the curriculum "could well provide the impetus for teachers to engage".
But a Government programme designed to co-ordinate the work of organisations supporting STEM had seen awareness and knowledge of the subjects increasing over its three-year lifetime, it added.