Corporal punishment is being used on severely disabled pupils in Scottish schools because staff do not know how to respond when students are in distress, MSPs have heard.
The improper use of restraint amounts to "at best institutional child abuse, at worst criminal assault", campaigners have said.
"Corporal punishment was banned in Scottish schools more than 30 years ago, but in our opinion failures in guidance and scrutiny have allowed some schools to effectively reintroduce it, illicitly, for disabled children," Beth Morrison, a Dundee parent, told the Scottish Parliament's Public Petitions Committee.
Ms Morrison's petition, which calls for new guidelines and an independent regulatory body to address concerns about restraint and seclusion, has attracted nearly 5,000 signatures and won support from children's rights campaigner Esther Rantzen.
Ms Morrison said: "Our children are often unable to say `I'm hungry, thirsty, tired or I'm in pain', and without the essential training and knowledge to understand the function of the behaviour, staff use restraint and seclusion to overpower the child using brute force - and this is completely unacceptable."
The problems were worst for children with complex needs, whether in special schools or mainstream schools with learning support bases, Ms Morrison told MSPs. "There are things that are happening to disabled children in schools that would not be accepted if those children were not disabled," she said.
Families had told Ms Morrison, for example, of children whose school wheelchairs had so many straps that they were "effectively being used as a mobile prison".
In a written statement, Ms Morrison said: "Sometimes, these little ones are pulled along or dragged by staff and thrown in alone to cool-down rooms which are very often bare, cell-like rooms where they are left to cry or until the behaviour stops."
Such cases were "part of a much wider failure of public policy in Scotland", she added, resulting from a "massive inconsistency" in practice across the 32 local authorities - and with no effective way for parents or professionals to challenge failings.
This, together with outdated policies, poor training and no specific remit for "care and dignity" in Education Scotland inspections, had created an "easy pathway for an abusive culture", Ms Morrison said.
Kate Sanger, a volunteer and family ambassador for the Challenging Behaviour Foundation charity, said it was "quite apparent" that school staff were poorly supported and lacked training to understand challenging behaviour.
She told the committee that "confrontational" responses could lead to both staff and children being injured, adding: "Seclusion doesn't actually teach the child anything - it's just used as a method of control."
Ian Hood, coordinator of Learning Disability Alliance Scotland, said that establishing an independent regulator was "really important", and that extending the remit of the Care Inspectorate or Education Scotland so that restraint and seclusion were better monitored "wouldn't take a lot".
The committee agreed to contact several organisations for views on the petition, including the Scottish government, the EIS teaching union, local authorities body Cosla and the office of the children's commissioner.
Deputy convener David Torrance said members feared that many of Scotland's most vulnerable children might face a "postcode lottery" around schools' use of restraint and seclusion.
A Scottish government spokeswoman said that training for teachers working with children with additional support needs had improved. She stressed that physical restraint should only be used when "absolutely necessary" and in the child's best interests.