The government's top social mobility adviser has quit, saying she was doing "more harm than good" in the role.
Katharine Birbalsingh, who has been dubbed Britain's strictest head teacher, has attracted controversy since being appointed in November 2021.
She said her "propensity to voice opinions that are considered controversial" was putting the commission "in jeopardy".
She added she had become increasingly cautious about what she said.
"Instead of going out there to bat for the team and celebrate our achievements, I am becoming a politician," she wrote in Schools Week magazine.
"And I can't bear the idea of ever being a politician. It just isn't who I am or a skillset I wish to develop," she added.
The government said Alun Francis, the principal of Oldham College, would replace Ms Birbalsingh on an interim basis, with arrangements for finding a permanent replacement announced in "due course".
In her inaugural speech as social mobility adviser, Ms Birbalsingh said the debate on social mobility was too focused on "rags-to-riches" stories of people from poor backgrounds getting into top universities and elite professions.
In her Schools Week article, she said the wider point of her speech had been lost amid "outrage" in the press, who she said had misconstrued her remarks and "insisted that I personally believe 'working class people should stay in their lane'".
She also came under fire last April for saying girls are less likely to choose physics A-level because it involves "hard maths" – later admitting her remarks had been "clunky".
The comments earned a rebuke from the Institute of Physics (IOP), which said it was concerned at the "continued use of outdated stereotypes".
In June last year, she criticised Boris Johnson, describing the former prime minister as a "bad role model for children" that sometimes didn't look "professional enough".
Ms Birbalsingh set up Michaela Community School in London in 2014, after losing her teaching job at another school after an outspoken speech to the 2010 Tory conference where she attacked a "culture of excuses and low standards" in the "broken" education system.
Her new school, part of the "free schools" initiative launched by the Conservative-Liberal Democrat coalition, has been described as the strictest in Britain.
In 2021, she was appointed chair of the government's social mobility commission, tasked with monitoring progress on improving life chances in England, by then equalities minister Liz Truss.
The advisory body is tasked with improving the number of children who go on to earn more or hold higher-status jobs than their parents. Research has suggested the UK has low rates of mobility compared to other developed countries.
Michaela Community School is known for its "tiger teaching" approach, where pupils are expected to adhere to strict rules on things like uniform, slouching, and talking in corridors.
In a resignation letter to Equalities Minister Kemi Badenoch, Ms Birbalsingh said she believed the approach would "make for good schools" if replicated elsewhere.
However, she said she she worried that any research the commission did that vindicated her approach would be "tainted" by association with her.
"People will imagine that something sinister is going on and that I am using the [commission] in order to prove a point with Michaela," she added.
In a letter of reply, Ms Badenoch praised her "fresh approach to social mobility", which had moved away from the idea "that it should just be about the 'long' upward mobility from the bottom to the top".
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