Christine Gilbert should leave Ofsted next year because "five years is enough" for her spell as chief schools inspector, according to her boss at the education watchdog.
Zenna Atkins, Ofsted's chair, was speaking exclusively to The TES in the week it was reported that the Government wants to install a new chief inspector.
Ms Atkins said Ms Gilbert should not seek to extend her contract when it ends next year.
"I think that 2011 does feel about right," she said. "It is exhausting putting this level of change into an organisation when you are changing systems, the processes, the structure, the people. Five years is enough."
Chris Woodhead, Ms Gilbert's most outspoken predecessor, served for more than six years as chief inspector before resigning.
Ms Gilbert has already told Education Secretary Michael Gove that she will not try to have her contract renewed when it expires in October 2011 and is prepared to discuss leaving earlier next year.
Ms Atkins started at Ofsted with Ms Gilbert in 2006 and their contracts run out at the same time. But the watchdog's first chairman will definitely depart early, this September, to take over from Anders Hultin as UK, Europe and Africa chief executive of GEMS, the international private schools chain.
She believes the company "hasn't made quite the footprint it should have made in the UK" and sees the Government's free schools policy as an opportunity to put that right, "too bloody exciting to miss".
A dyslexic who was unable to read until she was 12, was expelled and left school with a single O-level, she seems like an unlikely education boss. But by 2006, when she was picked to head the board overseeing Ofsted's expansion to take in children's social services, Ms Atkins had become, in her words, an "acclaimed social entrepreneur".
The 44-year-old describes Ofsted as a "business", inspections as "product" and is proud that the watchdog's cost to the taxpayer has been slashed by a third - #163;80 million - under her watch, leaving an organisation that "functions brilliantly".
Problems along the way included the aftermath of the Baby P scandal in Haringey, when Ofsted had to contradict its own data-based inspection, which concluded children's services in the London borough were "good". Ms Atkins said if it had been left to her, the data-based children's services inspections would have been replaced "far sooner".
She admits Ofsted's media profile has been a weakness. "The style of Ofsted under the leadership of Christine and my governance has been about, 'It's what you deliver and not about the story you are telling in the media,'" she said.