Ofsted may have "lost the trust of the profession" after dozens of complaints were made about the schools watchdog in Hertfordshire since 2020.
New data has revealed 40 complaints were recorded about inspections in the county's schools over the three years to March 2023, 30 of which were registered last year.
The government received 1,199 complaints nationwide, which the Association of School and College Leaders said "strongly suggests Ofsted has lost the trust of the profession".
Concerns were raised over the behaviour of inspectors in 502 cases, including 15 in Hertfordshire over a three-year period.
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Only one complaint in Hertfordshire and 18 across England were fully upheld last year. However, Ofsted was found to be partially in the wrong in 263 cases (six in Hertfordshire).
Its inspection process has come under greater scrutiny in the past year, after the suicide of headteacher Ruth Perry whose school was downgraded from the highest to the lowest rating over safeguarding concerns.
In January, the House of Commons Education Committee recommended Ofsted conduct an in-depth review of its complaints process, after hearing evidence the inspectorate was "marking its own homework".
The committee further heard evidence from school staff that the workload required to prepare for inspections can feel "crushing" and "relentless".
NAHT, a union for school leaders, said it welcomed measures to improve the complaints process last year, but it would still like to see an independent body handling them.
Paul Whiteman, NAHT general secretary, said: "More broadly, fundamental reform of the way Ofsted operates is urgently needed to improve the reliability and usefulness of inspections, while reducing the unacceptable toll on the wellbeing and mental health of leaders and teachers."
An Ofsted spokesperson said: "We want to make sure that our work is always carried out with professionalism, courtesy, empathy and respect. In the vast majority of cases it is – but we take all complaints very seriously.
"We understand that some have found our complaints process difficult to navigate, so we recently introduced a new, more transparent process, including the option for leaders to call a senior person at Ofsted if they have any concerns during their inspection. We consulted on these measures and they were strongly supported by the sectors we inspect."
The regulator said it will respond to the Education Committee's findings in the coming weeks.
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