Bristol City Council has confirmed that its education chief Heather Tomlinson is leaving.

Her departure, revealed in the Bristol Post last month, comes after four and half years in which she has led an unprecedented shake-up of schooling in the city.

Ms Tomlinson is taking early retirement from her £120,000-a-year post as strategic director of children, young people and skills.

She said: "The role of a director of children's services is extremely demanding in any authority. It is no secret that the role is particularly demanding in Bristol, particularly regarding standards in our schools. This feels like the right time for someone else to take the reins to lead children's services to the next level. "

The city council's chief executive Jan Ormondroyd today paid tribute to Ms Tomlinson's contribution to education in the city.

"I fully respect Heather's decision to move on and wish her the very best for the future. She leaves behind a strong management team, who will continue to work to improve school standards and protect vulnerable children and young people - and who will be supported by myself and the rest of the new strategic leadership team. We are now actively looking for an interim director, whilst planning the early recruitment of a permanent replacement."

Details of Ms Tomlinson's pay-off, agreed by councillors on Thursday, have not been disclosed but the National Union of Teachers has already said she must not be given a special deal.

Bristol divisional secretary Nina Franklin said: "Premature retirement compensation is not available to teachers and any of our members and I hope that there is to be no different treatment for a senior officer of the authority.

"I know that our members will be extremely angry about this if a deal is done as many of them have faced redundancy and only been able to take their basic pension."

Reactions to Ms Tomlinson's retirement so far have been mixed.

Councillor Peter Hammond, the Labour cabinet councillor for children, thanked her for her hard work and professionalism.

He said: "She has been able to lead Bristol's children's services through an intense period of change and we're now starting to see the benefits of this with an upward trend on results, new academies and arrangements for partnership working. It has been a pleasure to work with Heather and I hope she has a very enjoyable retirement."

Liberal Democrat spokeswoman Clare Campion-Smith said: "The city owes a real debt to Heather. She came at a time when raising educational standards in Bristol seemed an intractable problem. Now we are the 10th most improving authority. Young people in the city are leaving school with better qualifications.

"She is always the first to say that Bristol has a long way to go and that we must move faster along the road of school improvement. We must make sure we build on what Heather's vision and determination have achieved."

But Tory spokesman John Goulandris said progress on educational attainment had been "grindingly slow".

"Parents and pupils naturally apportion responsibility for this poor performance to those well-paid professionals charged with raising Bristol's education standards," he said.

Mr Goulandris added: "Whilst we have been critical of the departing strategic director, we would still like to thank her for her efforts over the past four-and-a-half years and wish her well.

"It is now essential that we look to the future and seek to appoint a top-calibre successor for what is a hugely challenging role."

Wansdyke Labour MP Dan Norris said Ms Tomlinson's period in charge had been an "unfortunate chapter" for Bristol and few would shed tears over her departure.