One in 10 academically promising state school pupils in England do not go on to university, a report has claimed.
The study also says thousands of bright pupils are let down by schools because they fall back after high levels of early achievement.
The report for education charity the Sutton Trust says 60,000 high achievers do not go on to university every year.
The government said it was determined that children's talents, no matter what their background, would not be wasted.
If you get A-levels you are as highly likely as any other pupil to subsequently enrol on a degree course
Sutton Trust report
The research, based on analysis of the attainment of pupils starting secondary school in 1997, tried to estimate the educational "attrition rates" of academically gifted pupils long before they think of applying for university.
It found the number of high-achieving state pupils shrank from about 88,000 at the age of 11, to just over 50,000 at age 16. Some 32,000 of these end up going to university.
It also found high rates of "leakage" among the least privileged of pupils - those qualifying for free school meals (FSM).
Two thirds of the top-performing pupils at age 11 were no longer in that category by the time they did their GCSEs. And half of these did not go on to university.
The report says: "The raw gap in higher education participation rates between pupils on free school meals and other pupils is stark."
It said non-FSM pupils had about a one in three chance of going to university while those on FSM had about a one in eight chance.
If all the missing 60,000 pupils had gone on to university, they would have boosted the participation rate by a quarter, the report added.
But the study had a positive message for those who did A-levels.
"If you get A-levels you are as highly likely as any other pupil to subsequently enrol on a degree course.
"The main problem in terms of widening access to higher education is getting non-traditional students to A-levels in the first place," it added.
The country's elite universities are being urged to increase the number state pupils that attend as undergraduates, and many are struggling to do so.
Dr Anna Vignoles, of the Institute of Education, who led the research said it had long been argued that financial and social barriers at the point of entry to higher education prevented them from going to university.
"This research shows clearly that the main reason why poorer students do not go to university to the same extent as their wealthier peers is that they have weaker academic achievement in school."
There are now around 300,000 more young people going to university than 10 years ago.
Higher Education Minister
Research director at the Sutton Trust, Dr Lee Elliot Major said the study showed there were significant numbers of bright young people with academic potential who do not progress to university.
"If we are serious about broadening the social mix of the sector it is important not only that the brightest and best get in to our most highly-selective institutions, but that more young people from poorer backgrounds go on to higher education full stop."
Higher Education Minister Bill Rammell said: "There are now around 300,000 more young people going to university than 10 years ago.
"Latest figures show that we are improving attainment across the board and the gap between children on free school meals and their peers getting five good GCSEs in 2007 had narrowed by four per cent since 2003.
"We are determined to continue this trend."
He added that a number of schemes linked up talented pupils in school with higher education students as mentors.
Shadow Universities Secretary David Willetts said the report confirmed his worst fears.
"Bright children from poorer backgrounds are being failed by the education system. It is a shocking waste of talent.
"Universities cannot make up for all the problems that occur early on. That is why we are committed to more good schools."