The move came as the chairman of Blackburn with Darwen's Governors' Forum claimed concerns had been expressed about the merger of the two special schools shortly after they joined.
Fernhurst School, Heys Lane, was created when Tullyallan and Bank Hey schools in Blackburn joined 15 months ago. It shut last week after Blackburn with Darwen Council claimed two stairwells had become unsafe.
The borough's children's services overview and scrutiny committee was told the council admitted that its decision to close the school had partly been based on concerns about the management of pupil movement and behaviour in certain parts of the building.
But it quashed rumours the school would never reopen, saying 14-16 year-olds had returned, while other years were being split across schools elsewhere in the borough.
They will return next term, after repairs are completed.
The report stated: "Consultation between us and staff has resulted in a decision not to use some parts of the building where clear and direct control cannot be easily achieved.
"This is generally the older parts of the building. Improved routines and timetabling have been introduced to reduce the amount of pupil movement between lessons which is known to have a positive impact."
But Jack Peet, chairman of the Governors' Forum, said: "Concerns about this were raised a long time ago and my concern is that it had to come to this."
Coun John Williams, a Tory councillor, said: "This should have been obvious before the merger. We need to make sure such obvious things haven't been overlooked elsewhere."
Coun Kevin Connor, said: "The task force we have set up will ask a lot of difficult questions to those in charge before we make recommendations about how this can be avoided in the future."
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