More pressure must be put on state schools to get pupils into the UK's top universities, MP and former Welsh Secretary Paul Murphy has urged.
Mr Murphy, tasked with getting more Welsh children into Oxford and Cambridge universities, partly blamed a lack of ambition among teachers.
The number of pupils accepted into Oxbridge is falling.
The Torfaen MP has also said he is worried the Welsh Baccalaureate might be a barrier.
Mr Murphy, who was appointed in the Oxbridge ambassador role by the Welsh government last month, said he believed fewer teachers in Wales had been to Oxford and Cambridge compared to 40 years ago so had less knowledge about getting pupils in.
"I'm sure there's lots of youngsters who would like to go but don't know how to go about it," he said.
"It's getting rid of the fear of the perceived elitism when they go there.
"Unless we up the pressure on schools and colleges in Wales to do this, then it's not going to do anything about it."
NUT Cymru Secretary David Evans said: "I think that every teacher wants to do the best by their pupils in all circumstances. And certainly, from my experience, teachers actually do encourage pupils who they think might be able to go to Oxford or Cambridge to apply."
One head teacher in Wales, who did not want to be identified, told BBC Wales News website there was little support on offer from the Welsh government for schools trying to get pupils into the very best universities.
"We need to make sure our very able students have the abilities to compete on a level playing field," he said.
"The Welsh government needs to be ambitious for our students to attend the best universities whether it's Oxford or Cambridge or the USA or growing our own universities."
Figures obtained by BBC Wales show the number of comprehensive pupils getting into Oxbridge has fallen from 96 in 2008 to 76 in 2012.
Figures also show the number of students from Wales' independent schools have remained stable for the same period - 28 in 2008 to 29 in 2012.
Conservative education spokesperson Angela Burns said there needed to be debate as to whether students were being pushed hard enough.
"The mood music coming out of Wales for the last couple of years has been pretty disastrous," she said.
"We talk about how we've failed in our international rankings, our pupils are consistently at the bottom of the tables.
"There may have been improvements but we're dropping behind the rest of the UK and Europe."
Mr Murphy has said students from the south Wales valleys are five times less likely to apply to Oxford or Cambridge than students in some of the more affluent English counties.
A report from his office a year ago highlighted a series of "challenges" in increasing the number of Welsh students at Oxbridge, including the Welsh Bacc, a qualification introduced about a decade ago to offer a more rounded education.
"Discussions with admissions tutors raised concerns with the Welsh Baccalaureate (WBQ)," said the report.
Questions had been raised over the quality and value of some WBQ components.
In fact, Oxford's undergraduate admissions director said it could put Welsh pupils at a disadvantage.
This is because prospective Oxford and Cambridge University students are usually expected to have studied three subjects at A-level.
However, many Welsh students doing the WBQ - compulsory in many schools - will only do two A-levels.
A recent report by Cardiff University suggested university students who studied the WBQ were less likely to get higher degrees than those who did not.
But the lack of Welsh state school pupils in Oxbridge and other top universities cannot simply be put down to the WBQ.
Dr Julia Paolitto, admissions and educational policy press officer for Oxford, said there were a number of factors, including a reluctance by some schools to encourage pupils to leave Wales, particularly Welsh medium schools.
The universities also pointed to exam results, which both said were arguably the biggest barrier.
This was also raised in Mr Murphy's report which said the Welsh government was trying to improve standards but that "provision for talented students is lacking".
"Further it has been reported that some students are often 'coached' to a C-grade at AS and A-level rather than attempting to produce higher quality answers," it said.
Unions deny teachers are not encouraging pupils enough.
NUT Cymru Secretary David Evans said: "I think that every teacher wants to do the best by their pupils in all circumstances.
"And certainly from my experience, teachers actually do encourage pupils who they think might be able to go to Oxford or Cambridge to apply."
The Welsh government said it wanted young people to aim high and that was why Mr Murphy had been appointed as Oxbridge ambassador.
He will be "a champion for Wales in opening doors to Oxbridge and ensuring that Oxbridge opportunities are not lost to those of our young people who would be best served by such a route".
The spokesperson added: "Following our recent review of qualifications we are in the process of revising our Welsh Baccalaureate Qualification to add rigour and ensure that is robust and fit for purpose.
"The review found broad support for the Welsh Baccalaureate, whilst also noting areas for strengthening the qualification."
Both Oxford and Cambridge say they have been working hard to attract Welsh pupils.
Both universities held a joint conference in Swansea last month. Some 1,260 pupils booked to attend with almost 80% from state schools.