Hundreds of children have been injured while being physically restrained in special schools, according to figures obtained by 5 live Investigates.
Some youngsters were pinned face-down on the floor, while others were strapped into chairs.
The figures revealed at least 731 injuries in the past three years.
The Department of Education says it plans to publish draft guidelines on reducing the need for restraint in special schools shortly.
A Freedom of Information request to local authorities in England, Scotland and Wales revealed 13,000 physical restraints in the past three years, resulting in 731 injuries.
But less than a fifth of authorities were able to provide the data - with most saying they didn't keep the information.
That suggests the true number of injuries caused by restraint in special schools is far higher.
Beth Morrison from Dundee launched a national campaign after her son Calum sustained injuries at his special school while being restrained.
She said she became worried when her son came home from school with bruising on his arms and spots on his chest consistent with haemorrhaging caused by being restrained.
The GP said there was some indication of positional asphyxia - such injuries are often seen in victims of strangulation - which was "very, very serious."
She says she was later told by an expert that the particular haemorrhaging on his chest could mean Calum had been held face-down, in a prone restraint.
The former care minister, Norman Lamb, has previously called for the technique to be banned in care settings, describing it as "dangerous".
Dundee Council told the BBC it was cooperating fully with a police investigation, and wouldn't comment on specific allegations until that has been completed.
The council said: "A report published last month by Education Scotland highlighted 'significant improvements' at the school.
"Inspectors said that 'there is a strong focus on ensuring the wellbeing of children and young people'."
The 5 live investigation found less than one fifth of local authorities in England, Scotland and Wales held any data about the use of restraint in special schools in their area.
In England, only nine out of 153 local authorities provided the BBC with figures. Of those that did, there were 6,262 reports of restraints, resulting in 360 injuries in the past three years
In Scotland, 17 out of 32 local authorities provided data, reporting 4,383 restraints and 157 injuries
In Wales, 11 out of 22 local authorities provided data, reporting 2,182 restraints and 214 injuries
The Education Authority of Northern Ireland told the BBC they did not hold the information
The Local Government Association said it takes safeguarding responsibilities "extremely seriously" but "the current system works on the basis that schools…have the primary responsibility".
They added that "where a specific safeguarding incident is raised, councils will act".
What is restraint?
'Reasonable force' can be used to keep people safe, prevent, damage to property or to prevent disorder. What is 'reasonable' is down to the judgement of the teacher, depending on individual circumstances. Using force as punishment is illegal.
[Source: Department for Education]
Mark Oldman is the head of Millgate School, a special school in Leicester for 11-16 year old boys who've been excluded from one or more other schools, mostly for physically and verbally abusing staff.
He says it's a tough environment - and restraint is sometimes needed.
"I've been physically attacked; pupils have attempted to hurt me or members of staff," he said.
"I've been bitten, spat at; I've been run at with an axe. But as their teacher, I have a responsibility to keep them safe, and sometimes that means using restraint.
"You have to be able to trust [school staff] to make snap decisions in some very difficult circumstances.
"I would say that 99.9% of the time, we get it right."
But Sir Stephen Bubb - who headed the investigation into the abuse of patients with learning disabilities and autism at Winterbourne View near Bristol - said the findings were "scandalous and very dangerous".
He now plans to ask the Children's Commissioner for England, Anne Longfield, to launch an inquiry.
"What is happening in local authorities is extraordinary," he said.
"Restraint appears to be widespread, but how do we know whether physical restraint is being used as a punishment, which is actually unlawful?"