Too many parents are challenging head teachers who discipline their children, a union leader says.
Excluded children returned to school 'on flimsy grounds', David Hart said
David Hart of the National Association of Head Teachers criticised their "extreme use" of procedures which he said put heads "in the dock".
They used human rights legislation to help create a "culture of challenge".
Appeals panels were still reinstating excluded pupils on "flimsy grounds", damaging the "law-abiding majority" of children, Mr Hart added.
He told a conference at the Barbican Centre, London: "Heads who seek to enforce discipline are entitled to the full support of governing bodies and education officers.
"Too often LEAs [local education authorities] are intimidated by lawyers, barrack room or real, or by self-appointed pressure groups, waving the civil libertarian flag and threatening damages or other mayhem.
"This spreads to independent appeal panels which are still reinstating on flimsy grounds."
It is not the first time Mr Hart has criticised parents.
Last year, he said too many families condoned truancy and claimed too many children lacked "good parental role models".
Some families condemned their children to a life of crime, he added.