[10] Parents sought a judicial review of Önaç's approach to special needs provision, but in December 2009 he resigned from his post soon after the legal action started.
On 11 May 2016 a petition was set up by students in the school objecting to new, harder sixth form entry requirements; it gained over 1,000 signatures in two days.
About the same time it emerged that Önaç and bursar Alan Wooley had set up a business earlier in the year, with the knowledge of the governors, where they were registered as the sole shareholders.
[24] On 19 October 2017 the new chair of governors, Paul Wright, announced that the head teacher had been suspended "without prejudice" while an inquiry ("in respect of concerns that have been raised over recent weeks") by the London Borough of Bromley took place.
[28][29] Freedom of Information requests revealed that 72 students had been forced out of the school during their A-level studies since Önaç became head in the 2010–2011 academic year.
[27] The report of Bromley council's independent inquiry, led by educationalist Christine Whatford, was published in July 2018, and accused St Olave's of illegally treating its students as "collateral damage" in the pursuit of its own interests.
The report also questioned Önaç's claims that he did not know the exclusions were potentially illegal, and criticised the school's financial management.
"[31] On 11-14 September 2023 a Teaching Regulation Agency teacher misconduct hearing was held regarding Önaç's tenure at St Olave's.
The panel found Önaç was guilty of serious misconduct "which fell significantly short of the standards expected of the profession", amounting to "unacceptable professional conduct".