It has long been the norm for schools to enter their brightest pupils for exams early, but the practice could be hampering the chances of high-flying students who want to study medicine at university, independent schools have warned.
A strict requirement laid down by many medical schools means that only results from Year 13 exams count for admissions. This is making schools wary of pupils sitting A levels early, according to the Independent Schools' Universities Committee.
Schools claim this is a particular problem in maths and is resulting in talented students having to endure "pedestrian" courses that do not provide sufficient challenge. Schools are stopping pupils sitting A-level maths in Year 12 and then further maths in Year 13 amid fears that this could result in a lower grade being considered by universities.
Roberta Georghiou, co-chair of the committee, has written to former government STEM (science, technology, engineering and maths) adviser Sir John Holman, who is an influential maths and science campaigner, claiming that the current situation is "disadvantaging the brightest students".
Ms Georghiou, head of Bury Grammar School for Girls in Greater Manchester, said talented pupils should be able to progress with the subject at their own pace. She has warned that a handful of medical schools are "dictating" how schools organise their maths curriculum at A level.
"Pupils and parents are thinking that it is not worth the risk of taking further maths because it is harder and they might get a B, and that would be the grade that counted," she told TES. "It is entirely in the interests of mathematicians and engineers and many scientists that mathematics should be taken early to allow for extension afterwards.
"These students are usually taught in the same groups as medical students and so, with greatest reluctance, schools will have to adopt a more pedestrian route through mathematics in the interests of some prospective medical students."
Ms Georghiou said there should be "flexibility" in how A-level maths is approached, but said that would only happen if medical schools were willing to accept it.
"Effectively, a few medical schools are determining how mathematics should be delivered in schools," she said. "It seems wrong if the outcome is less challenging maths courses."
Teachers are concerned about pupils being at even a slight disadvantage because medicine is an intensively competitive subject, with some universities receiving several thousand applications for just a few hundred places. Ms Georghiou also raised concerns that some schools may be unaware of the rules, meaning their pupils are disadvantaged further.
Some universities introduced the rule for medicine, dentistry and veterinary courses because of fears over excessive retakes and a "bite-size" culture of accumulating exam modules. They also argue that taking all the exams together prepares applicants for the high workload of the courses.
A spokesman for the Medical Schools Council said that it thought about a third of undergraduate medical programmes followed the policy, including the University of Nottingham and Queen Mary, University of London.
Documents from University College London explaining the rule say that, while A levels completed outside the normal time frame would not count in the offer, they would "of course be considered as part of the overall educational background" of a candidate.