Not enough fluent Welsh speakers from north Wales are being accepted for the National Professional Qualification for Headship (NPQH), it will be claimed today .
Bangor headteacher Wil Parry will voice "grave concern" over a lack of strong Welsh-speaking candidates from Gwynedd and neighbouring counties, on the opening day of the annual conference of Welsh-medium teachers' union UCAC.
He will call on the Assembly government to launch an immediate review into the geographic and linguistic background of candidates selected for the qualification - which all first-time heads must now hold. Latest figures for the 2005-6 NPQH intake reveal that 56.4 per cent of Welsh-speaking applicants were accepted on to the course, compared with only 50.4 per cent of monoglot applicants.
Overall, there were 121 non-Welsh speakers and 31 Welsh speakers accepted, with Welsh speakers making up a fifth of the total. Around three in 10 schools in Wales are Welsh medium.
Mr Parry, head of Ysgol Glan Cegin in Bangor, and a member of UCAC's general executive, said standards of bilingualism differed greatly across Wales.
He said that heads in the traditional Welsh-speaking counties of north Wales needed to be fully bilingual for the sake of school standards - and the community.
"I am not asking for favourable treatment for Welsh speakers or for a drop in standards," he said.
"Unless more strong Welsh-speaking candidates are accepted, we will not be able to fill the shoes of an ageing population of heads in Gwynedd and neighbouring counties."
He added: "If my figures are right, there was just one fully bilingual candidate from Gwynedd on the last intake."
The NPQH became compulsory for aspiring heads in Wales last September.
Headship training programmes are now funded by the Assembly government from a ring-fenced pound;1.55 million budget.
UCAC's conference, being held at the Celtic Hotel in Caernarfon, may also challenge the Assembly government's new definition of what constitutes a Welsh-medium school, which is based on the number of subjects studied via the language of heaven.
Elaine Edwards, UCAC's policy officer, will propose that the present draft definition - put out to consultation earlier this year - remains unclear and ambiguous.
A task force, headed by the Welsh Language Board, was asked to come up with a clearer definition more than two years ago. Delegates will also be told how the Welsh language, as a teaching and learning medium in Wales, is still given low priority by some councils.
Other motions at the conference raise concerns about the rising number of directors of education who lack an education background and have wide-ranging responsibilities in addition to education; and the use of external exam invigilators rather than teachers to monitor exam halls.
Gruff Hughes, who will be attending his first UCAC annual conference as general secretary, said: "With so many changes and pressures on education, it is essential that whoever leads on education must have it as their only portfolio and priority.
"Education is too important to be shared."
UCAC's newly-inaugurated national president, Gwyn Morris, will propose that examination boards should ensure pupils have the best conditions possible when sitting exams, including supervision by qualified teachers.
The national workload agreement, which UCAC did not sign, has removed exam invigilation from teachers' duties. The conference closes tomorrow.