Universities could increasingly introduce their own admissions tests for sixth-formers as a result of the Government's decision to break the link between AS and A-levels, it has been suggested.
Private school heads indicated that top institutions will need to find new ways of filtering out the best candidates.
But the move could unintentionally put privately-educated pupils at an advantage to their state school peers if they have access to more help and support needed to prepare for these tests.
Under major exams reforms announced by Education Secretary Michael Gove, AS-levels will no longer count towards final A-level grades, and will become a standalone qualifications.
A-levels will revert to traditional two-year courses, with final exams at the end.
Speaking as the Headmasters' and Headmistresses' Conference (HMC) met for their annual meeting in London, Peter Hamilton, headmaster of Haberdashers' Aske's Boys' School in Hertfordshire, questioned how popular the new-style AS-levels will be, saying it will depend in part on the value that universities place on them.
He said he would not be surprised if it became the norm for students to study for three A-levels, with time left over for other work.
"It could be extension work, it also could be very significantly, preparation for university entrance exams because they're coming in more and more," he said.
Currently, many top medical schools ask would-be students to sit additional tests, with the UKCAT and BMAT aptitude tests among the best known.
Some top universities, in particular Oxford and Cambridge, also already ask applicants to take additional tests in subjects such as maths and law, it was suggested.
Chris Ramsey, head of the King's School, Chester, said: "It's more likely that the most competitive universities will introduce more admissions tests because there isn't AS to give them a guide to attainment at the lower sixth level."
He suggested that a would-be medic for example, may in future do three A-levels in science and maths and spend their remaining time doing preparation work for medical aptitude tests.
Mr Ramsey said that medical schools in particular are faced with the difficult task of deciding which candidates to accept.
"If you take another piece of actual, real objective data away, the risk is either that they will set more tests, or it will become more of a lottery," he said.
Mr Hamilton indicated that independent schools will find it easier to help support students preparing for university admissions tests.
State schools face different pressures on funding and resources, it was suggested.
Universities are continually looking for ways to find the best candidates, and that whatever institutions have wanted, private schools have found it "easier to adapt and respond", Mr Hamilton said.
Mr Ramsey added: "The more complex the entry system, the more it advantages people who have the resources to cope with it."