An emergency team of heads and deputies took control of Ashburton High School in Croydon this week after a Government inspectors' report said the school was failing to provide an adequate education.
Headteacher Chris Hiscock has been seconded to Croydon education services so George Varnava, former National Association of Head Teachers' president and former head of Norwood School in Lambeth, can take his place. A permanent new head will be appointed in August next year.
Croydon's acting education director, David Sands, said Mr Hiscock had committed himself 100 per cent to the school during his 21Z2-year stay, and the authority was anxious to retain his skills.
But he continued: "The school has reached a situation whereby the education authority and governors could no longer avoid taking steps to arrest the decline in the school's roll.
"Parental confidence in Ashburton has fallen in the past couple of years and despite the hard work of the staff to improve classroom efforts, the behaviour of some pupils might at best be described as boisterous. Others would be more critical and it would be difficult not to agree with them.
"Our intention in taking resolute action is to restore the school's good reputation. In Mr Varnava we have been fortunate to attract an experienced head who is held in high esteem within the national education scene.
"He previously taught at Pimlico School where he was deputy head and at Holland Park, both recognised as successful inner city schools."
Mr Sands said Ashburton was a "very difficult" school with a significant number of pupils with special needs from poor backgrounds.
The biggest problem in the 900-pupil school is bullying which, says Croydon, is much worse than in many similar schools.
Ashburton failed an Office for Standards in Education inspection a year ago, and inspectors reported two months ago that there had been insufficient progress.
However, Croydon stressed that examination results had improved since the OFSTED report - 18 per cent of pupils have achieved five GCSEs with grades A to C, an increase of 5 per cent.