Darlington council is investigating Karen Pemberton's management of Eastbourne school after it carried out a survey that uncovered serious behaviour problems and found some students lived in fear of attacks between lessons.
In the survey of pupil and staff perceptions of the school, one student said: "I feel sad I might get hurt, knocked over or bashed in the face."
"Missiles are fired - coins and bottles," another added.
The report shocked the local authority which celebrated the school's removal from special measures just four months ago.
After forming a federation with the nearby Hurworth school, and receiving a pound;2 million boost from the Government, a record 33 per cent of pupils achieved five Cs or better at GCSE.
At the time, John Williams, the council leader, said: "In Karen Pemberton, Eastbourne school has an inspirational headteacher."
The report was commissioned as part of plans to dismantle the federation, which was believed to have served its purpose.
Some staff said attendance and behaviour had improved greatly since the school was placed in special measures. But others said it "felt like a battle most of the time" and reported that pupils were more disrespectful than ever.
Nearly a third of pupils said they had been bullied, although only 5 per cent of teachers acknowledged it as a problem.
The report said behaviour control systems were ineffective because staff were overwhelmed by the bureaucracy and by the scale of the problem.
Teachers believed there were too many supply staff who were unsure of what to do, while governors called the school fragile.
Attendance rates rose after security cameras were installed to prevent pupils walking out of school but significant numbers of pupils were still failing to turn up for lessons.
Ms Pemberton was unavailable for comment.
In a report which took the school out of special measures last year, Ofsted said that pupils were kept under close supervision and that exclusions had fallen substantially.
But inspectors said a few pupils created difficulties where teaching was less effective.