Leading educationalists are treating Wales as a "stepping stone" on their career paths, a teaching union leader has claimed.
Rex Phillips, Wales organiser of the NASUWT, said the sudden departure of Professor David Hawker from the Department for Children, Education, Lifelong Learning and Skills (DCELLS) highlights a "worrying lack of commitment" from top education figures.
Professor Hawker will leave DCELLS in September after less than two years as its director-general. He is going on secondment to the Department for Education in London to review English education quangos.
His predecessor Steve Marshall also left the post after less than two years to pursue a "dream job" in Canada, while in February Estyn chief inspector Dr Bill Maxwell left after just two years to take up the "exciting" role of senior chief inspector in his native Scotland.
Mr Phillips said: "Are people using Wales as a stepping stone for their careers? There doesn't seem to be much commitment.
"It's concerning that people don't seem to stay very long here. We should look for someone who has commitment to stay the course."
Dr Philip Dixon, director of the Association of Teachers and Lecturers Cymru, suggested the Assembly should stop looking for "outsiders" to solve Wales's problems and start making key appointments from within.
Professor Hawker's successor will be the fifth person to lead the Assembly government's education department in the last five years, following Richard Davies, Steve Marshall and interim chief Dennis Gunning.
This turnover has prompted concerns about a lack of stability and leadership at a time when Wales is going through huge educational change.
Paul Davies, Conservative shadow education minister, said: "This brings tremendous uncertainty to the implementation of government policies.
"I am looking to the minister to reassure teachers, students and parents across Wales that turbulent times in the government's education department will not negatively impact on work to raise educational standards."
Liberal Democrat education spokeswoman Jenny Randerson said: "The high turnover of director-generals in the education department suggests that all is not well.
"With rising child poverty levels and a high number of young people not in education, employment or training, Wales can ill afford this revolving door.
"Frequent change at the top is destabilising and requires strong leadership from the minister."
David Evans, secretary of NUT Cymru, said: "We need stability in DCELLS and a strong hand on the tiller - someone who's going to be in this extremely key role for the long term."
An Assembly government spokesman said: "Clearly, there will be arrangements in place to ensure a smooth transition following the departure of David Hawker."
Although he cited personal reasons for his "unexpected" departure, TES Cymru understands Professor Hawker had been planning to leave DCELLS for some time, following a falling-out with education minister Leighton Andrews.
John Osmond, director of the Institute of Welsh Affairs (IWA), an independent think-tank, has claimed the episode revealed a "personality clash" at the heart of government policy.
Writing in the IWA's online magazine last week, Mr Osmond said: "Leighton Andrews's more abrasive qualities undoubtedly changed the atmosphere within the department."
An Assembly government spokesperson dismissed the allegations as "absolute nonsense".
Original headline: Unions accuse education chiefs of using Wales as career `stepping stone'