The Postgraduate Dean of the Wales Deanery, Professor Derek Gallan told members of the Health and Social Care Committee that in some cases the Deanery was "unable to properly train" students to the standards required by the General Medical Council (GMC).
He was giving evidence to the committee on 10 January 2013.
Members of the health committee heard about plans to change the way that doctors and dentists are trained during a session on the reconfiguration of the NHS in Wales.
Professor Derek Gallen said that some medical specialties would in future be taught on a reduced number of sites in order to deliver the appropriate training.
"Our business is still the education and training of doctors - and we are not currently fulfilling that to the standards required by the GMC," said Professor Gallen.
"We are unable to properly train and that is the reason why we need less sites, better rotas and professionalise our educators."
Committee members were also updated on the work being done by the National Clinical Forum (NCF) to monitor health board plans to reconfigure services across Wales.
The forum was set up in 2011 by Health Minister Lesley Griffiths to give independent expert advice to the assembly on the expected effects of the reconfiguration proposals.
The chair of the forum Professor Michael Harmer was questioned by the Conservative AM Darren Millar on why an independent report criticising NHS changes in north Wales was
rewritten by the NCF after being submitted
Professor Harmer admitted that "on the surface it seems totally bizarre that that happened".
He then explained to Mr Millar that the NCF had initially written its report criticising the health board for not including plans for the future use of district general hospitals in north Wales.
He said that the NCF initially criticised Betsi Cadwaladr University Health Board for omitting that information, but later amended the report.
This was after it became clear to him and colleagues that the decision for the omission was a deliberate one and that information on the board's plans for its district hospitals would be published subsequently.