The overall effectiveness of a boys' secondary school has been rated "requires improvement" by education chiefs.
William Ellis School, in Highgate Road, was downgraded from "good" following an inspection by Ofsted in May.
The quality of education, behaviour and attitudes and leadership and management all fell from "good" in 2017 to "requires improvement", while personal development and sixth form provision remained "good".
Headteacher Izzy Jones said in a letter to parents that she was "committed to William Ellis’s journey of improvement" and that she had submitted a formal complaint to Ofsted about the inspection and outcome.
"Whilst we are pleased to receive ‘good’ judgements for personal development and sixth form provision, we are very disappointed that overall, the progress we have made in recent years was not recognised, especially given the challenges of the pandemic and its disruptive effects on the school across 2020, 2021 and 2022," she said.
Inspectors highlighted the strength of modern languages, saying pupils’ progression towards ambitious goals is "carefully planned for and supported", but said this is "not consistent" across subjects and year groups, which over time "leads to unevenness in the quality of pupils’ work".
New provision for special educational needs or disability (SEND) was praised with pupils receiving "a range of additional support".
A concern for inspectors was pupil behaviour, with learning time "lost to low-level disruption in Years 7 to 11" and "disorderly behaviour in the corridors not dealt with consistently by staff".
They said while students felt safe, "some feel unable to share concerns with staff and others reported feeling worried about behaviour around the school, including the use of derogatory language".
The report added that pupils "do not behave consistently well".
"Leaders need to take effective steps to improve behaviour and ensure that staff follow agreed policies and procedures," wrote inspectors. "This includes responding appropriately to incidents of derogatory language."
Ms Jones said: "Since September 2020 we have worked hard to raise students’ awareness of why this language is problematic and should not be used under any circumstances."
The school has already tightened restrictions on mobile phone use, re-establishing uniform regulation and monitoring corridors.
She said the "complexity and depth" of the challenges faced by pupils during Covid lockdown school closures "was far more profound than we anticipated, and our response must rise to the challenge that this presents".
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