INSPECTORS found staff locking classroom doors at a special school to stop pupils walking out of lessons.
Woodlands School, in Beechdale Road, Aspley, was judged "inadequate" by Ofsted after the discovery last month and has been put in special measures.
Inspectors published their findings after visiting the school on June 18 and 19.
They said the school did not "adequately safeguard pupils" because some classroom doors were "routinely locked".
The report also said some staff responses to low-level disruptive behaviour were "unsuitable".
In a statement, the school said it was "profoundly disappointed" by the result of the inspection and it had already dealt with all the problems raised.
The school has 56 pupils aged three to 16, including some with learning difficulties and others with behavioural and emotional problems.
Executive head teacher John Dyson said that when staff had locked the doors, they had remained in the room, with the key, at all times and children were not in danger.
"We can make excuses and say perhaps it was the pressure of the inspection on the day but we are profoundly put out that we did not get it right for the pupils and the local community."
Locks on internal doors had already been removed, he said. "We recognise that mistake but it's not endemic in the school in any shape or form."
The school will now be subject to extra monitoring and has drawn up a plan for improvement.
The inspectors also said that teaching had been improving at the school and an increasing amount had been "good or better".
Mr Dyson said the school hoped to be out of special measures by January.
In a statement, the school also said: "We would hope that a balance of opinion about the school could be demonstrated during this challenging time.
"The inspection report contains many contradictions which in themselves illustrate the difficult decision that inspectors had in making their final judgement.
"There was no inadequate teaching in the school and 80 per cent of the lessons graded were good or better."
It also assured parents and pupils that staff and governors were determined to make improvements.
Councillor David Mellen, city council portfolio holder for children services, said: "The council is confident that the school has taken appropriate steps since the inspection to address the issues raised in the report.
"Effective measures are in place to ensure that pupils are maintained safely within school.
"Pupils report that they feel safe in school and parental views support this."
