State schools are not doing enough to push their brightest pupils, it has been suggested.
In an interview with BBC Radio 4, Mike Nicholson, head of undergraduate admissions at Oxford University, claimed that schools are focusing too much attention on lifting pupils from D grades to C grades, rather than encouraging "solid B" students to perform better.
This "target-driven" culture means capable youngsters are missing out on places at the country's best universities, he noted.
"GCSE performance is one of the few indicators used to demonstrate school success. Schools wanting to ensure they are well-placed will make every effort to get as many students who are going to get C grades to get C grades. Any student who might get a D grade, they'll put some extra effort into trying to get those students up to a C grade," Mr Nicholson explained.
"Maybe there are students who are being missed, who have got a solid B potential and aren't in any danger of dropping below that C grade that's going to get the school an extra percentage point on their performance figures. That's the group of students who could be being disadvantaged."
Figures published by Ucas this week show that university applications are on the rise, with students rushing to gain places before tuition fees are increased in 2012.