Wales's chief education official is leaving after less than two years in the job, prompting concerns about the ability of the Government to deliver key school reforms.
David Hawker, director general of the Department for Children, Education and Lifelong Learning (DCELL), is leaving in September amid rumours of differences of opinion with minister Leighton Andrews.
In a letter seen by TES Cymru, Professor Hawker said the reason for his "sudden and unexpected" departure was the need to be closer to his wife, who is suffering from ill health, at their home in Sussex.
But Professor Hawker's successor will be the fifth person to lead the education department in the last five years, a situation that has been branded "shambolic" by critics.
One leading educationalist, who did not want to be named, said: "If such a situation occurred at school or local authority level, the inspectorate would be asked to see if the organisation concerned needed to go into special measures.
"Surely the appropriate Assembly committee now needs to undertake an urgent inquiry into the performance and leadership of DCELL.
"Ten years ago Wales was the envy of many other countries - now it looks as if it is becoming an educational basket case."
Dr Philip Dixon, director of teaching union ATL Cymru, said: "Serious questions must be asked about why Wales can't keep directors of education. Are there problems in DCELL that need to be addressed? We need stability."
In his letter, Professor Hawker said he was "sorry" to be leaving Wales after a two-year stint that he found "challenging, absorbing, and for the most part immensely enjoyable".
He said he had "every intention of staying several years longer" if not for his personal circumstances.
"I leave with a genuine sense of achievement, and a confidence that we are now well on course to deliver the ambitious agenda we have set ourselves," he wrote. However, rumours have been circulating that Professor Hawker was not happy at DCELL.
TES Cymru understands Professor Hawker recently had a falling out with Leighton Andrews, the education minister, over differences on a number of education policies, including free school breakfasts and school reorganisation.
A source said the pair recently had a "fantastic stand-up row" over the direction of the attainment-raising School Effectiveness Framework (SEF) and how many areas it should focus on in front of shocked civil servants. "I'm not surprised he has gone; this has been on the cards for a while," he said.
Another source said: "The two of them fell out badly. The situation was getting dire. People are rightly wondering did he jump or was he pushed?"
Educationalists have suggested that Chris Tweedale, currently director of the Assembly government's school effectiveness group, is being lined up to take over the top job.
Assembly government permanent secretary Gill Morgan paid tribute to Professor Hawker, who is going on a secondment to the Department for Education in London.
She said: "I know that everyone who's worked with David over the past two years will join me in thanking him for the enthusiasm, commitment and expertise he's brought to the job. I wish David every success in his new role."
David Reynolds, professor of education at the University of Plymouth and a former Assembly government advisor, said: "I feel sorry for Professor Hawker because he has been in the middle of difficult circumstances; beset by financial issues and a minister keen to make his mark quickly."
Brian Lightman, general secretary-elect of heads union ASCL, said: "We're very sorry to be losing David Hawker at such a crucial time for education in Wales, with SEF and the new inspection framework coming in. We hope it will be possible to find some continuity at DCELL."
An Assembly government spokesman denied the allegations of rows between Professor Hawker and Mr Andrews, describing them as "absolute nonsense".
"The reality is very much the opposite," he said. "There is complete alignment with the position of the education minister and all of his officials on the way forward for the School Effectiveness Framework."