A shortage of Welsh-speaking teachers and lecturers is holding back the growth of Welsh-medium courses and qualifications.
And the situation is worsened by the fact that those who trained in Welsh often took jobs in other fields, according to Dr Heledd Hayes, education officer at the NUT Cymru.
Inspectorate Estyn believes more Welsh-medium and bilingual courses must be made available for 14 to 19-year-olds, and it has identified the shortage of suitable teachers as a major obstacle.
The inspection body also points to a lack of Welsh-medium examiners and resources such as textbooks, as well as the small take-up of some courses. The report into bilingual education for teenagers over 14 criticises some 14-19 networks for not earmarking enough cash for the extension of Welsh-language media.
In 2004-5, just 5 per cent of further education staff taught in the Welsh language, while secondary schools fared better - 12 per cent in 2005-6.
Growth has been slow. Trainee teachers who study in Welsh often choose not to work in the Welsh-language sector. And there has been a lukewarm response to a government-funded sabbatical scheme offering free Welsh tuition.
Since 2006, just 99 teachers have attended the courses in Bangor and Cardiff. Plans to introduce a third location in Mid Wales were abandoned after budget cuts.
Gruff Hughes, general secretary of the Welsh-medium teaching union UCAC, said there had been some progress. "It's still 99 more than we had," he said. "There is a need for more teachers in specific areas. I'm only aware of one Welsh-medium cookery course, for example."
Dr Hayes said teaching was now competing with other employers, such as the media, for Welsh-speaking staff.
"They are scooping up a lot of talent," said Dr Hayes, who believes an increase in Welsh-medium courses has left demand for teachers outstripping supply.
"It's important that initiatives increase and people are aware of them," she said. "A lot of teachers didn't know about the sabbatical."
The number of Welsh-medium courses rose by 13 per cent to 705 between 2003 and 2005, but there are still far more available in English - especially in vocational subjects. Courses are inadequate in areas such as IT and economics.
Previous Estyn inspections found important shortcomings in bilingual provision in almost half of the secondary schools and training providers seen in 2005-6 and 2006-7. The body also noted significant regional variations in course availability, often reflecting language patterns throughout Wales.
Gareth Jones, assistant head at Brecon High in Powys, said the recruitment of Welsh-medium staff was "a problem in an Anglicised area". He added: "We can offer Welsh-medium courses in some areas up to age 16, but we don't have the expertise to offer A-levels."
Estyn wants targets set, new courses, a broader sabbatical scheme and greater collaboration between providers and the use of peripatetic teachers and technology in sparsely populated areas.
COLLEGE TAKES LEAD FROM EMPLOYERS
Estyn singled out Anglesey and Gwynedd for being at the forefront of bilingual course expansion - 50 per cent growth in 2004-5 compared with decline elsewhere.
But this northern corner of Wales has a high number of Welsh speakers - about 75 per cent of the population, says Dr Haydn Edwards, principal at Coleg Menai, based at Bangor and Llangefni. The college has large numbers of Welsh-speaking staff - around 72 per cent of lecturers are bilingual.
"Employers determine what we do, and different sectors want bilingualism," said Dr Edwards.
Coleg Menai holds bilingualism workshops and awards prizes for achievement. Staff receive support to improve their Welsh, and a conversation club aims to build confidence. Managers are expected to deal with one agenda item at every meeting in Welsh. Those with less confidence receive an email containing key words.
Dr Edwards said recruiting teaching staff had not been a problem. "The government should have a strategy on bilingualism for schools and colleges," he said.