Almost one child a week has needed medical treatment after being physically restrained at a privately-run children's prison, figures show.
More than 100 children needed to have wounds - including nose bleeds, bruising and sprains - looked at after being restrained by staff at Medway Secure Training Centre in the two years to 2009.
The Howard League for Penal Reform, which released the statistics, has condemned the use of physical restraint.
It believes government inspectors Ofsted need to change the way it assesses secure training centres (STC), which are run by private companies.
The Howard League's director Frances Crook said: "To use physical violence on children which can inflict injuries is not the way to teach them how to behave.
"It is also absolutely terrifying to have grown ups hold you down if you refuse to go to your room of if you're not doing what they're telling you to do.
"We're not saying Ofsted should not do the inspections, but they're not doing them right.
"They have got to radically change the way they are inspecting these places.
"They should be willing to be more critical of what goes on in these prisons for children, which are run by private companies who make a profit."
Ofsted last inspected Medway STC, in Sir Evelyn Road, Rochester, in September and rated the overall quality as good. Inspectors said records showed incidents of physical restraint had decreased by more than 50 per cent in the past five months.
But the Howard League, which believes STCs should be shut down, believes Ofsted needs to be more critical.
A spokesman for Ofsted said: "The Howard League for Penal Reform has a long established view that secure training centres should be closed, and Ofsted respects this.
"However, our responsibility is to inspect and report on the evidence.
"The use of restraint is something that we scrutinise rigorously at every inspection.
"We extensively review records of restraint, including the viewing of CCTV footage."