Ofsted has begun an unannounced inspection at a school where there have been two days of walkouts by staff following safeguarding concerns.
Inspectors visited Starbank School in the Yardley area of Birmingham yesterday, and were at the site again today.
They will be publishing their findings in due course, Ofsted added.
The move followed two separate days of industrial action by members of the NASUWT teaching union, which had called for a knife audit at the school and raised concerns over pupil behaviour.
Staff and teachers staged the second of the strikes today.
There was no picket line, as the union said members were meeting privately to discuss "all the outstanding issues" that remain unresolved between them and school leaders and Birmingham City Council representatives.
Last week, about 20 members of the NASUWT joined a picket at the school's Hob Moor Road site to express their concerns about pupil "indiscipline" and staff safeguarding measures.
The action came following reports a 12-inch knife had been brought into the school, and a separate incident where a member of staff is said to have been assaulted.
The school, rated "outstanding" by Ofsted in May 2012, is also reported to have a problem with pupils fighting each Thursday.
In a statement, Ofsted said: "[Inspectors] began an unannounced inspection of this school yesterday."