Many of Wales's first-time heads may not be the best candidates for the job, an education chief has warned.
Karl Napieralla, of the Association of Directors of Education Wales, said the National Professional Qualification for Headship (NPQH) was failing to attract or deliver the best school leaders.
His comments, made during an Assembly committee meeting, came as Wales faces a headteacher recruitment crisis.
Latest figures from the General Teaching Council for Wales show a third of heads are aged 55 or over and likely to retire in the next couple of years.
Mr Napieralla, director of education at Neath Port Talbot, told TES Cymru it was time for a review of the headship qualification.
"If (the NPQH) was a successful qualification, we would have far more quality applications," he said.
But heads' unions said many deputy and assistant heads who held the qualification were loath to step up because of increased workload, seeing other senior roles as less stressful options with good pay.
The Assembly government-managed headship programme has been a mandatory qualification for all first-time heads appointed in Wales since September 2005.
The course, which costs Pounds 3,000 and takes 12-20 months to complete, covers six key areas relating to headship. To date, 436 in-service heads now have the qualification.
But Gareth Jones, secretary of heads' union ASCL Cymru, said the programme needed to become more practical and include more legal, health and safety, and financial management training.
But he said newly appointed heads were competent in their jobs.
The National Union of Teachers Cymru called for the headship qualification to be made an optional requirement for aspiring heads.
Dr Heledd Hayes, of the NUT, said it would be "sensible" to review the qualification. "It's been going for some years now, and as skills change and develop, we should look at it again," she said.
The programme was last revised in January 2006.
A spokeswoman for the Assembly government said Estyn, the Welsh inspectorate, would review the qualification in 2009, and its advice would be used to commission a new contract to refresh and deliver the NPQH from 2010.
Research would also be carried out into why some holders of the NPQH are not applying for headship, she said.