The scheme, to be piloted in three areas of England and Wales, will alert parents to convicted paedophiles living on nearby streets and next to playgrounds and school routes.
It is a version of Megan's Law, which was launched in the US following the rape and killing of seven-year-old Megan Kanka in New Jersey in 1994. But headteachers fear it will mean a return to the vigilante action of 2000, which followed the News of the World's "name and shame" campaign, in response to the murder of eight-year-old Sarah Payne by a convicted child molester.
Martin Ward, deputy general secretary of the Association of School and College Leaders, said the measures were not "necessary or helpful".
He said: "It could cause these people to move out from supervised circumstances and it raises the prospect of innocent people being targeted."
Mr Ward said the scheme, which makes only general information rather than names and addresses available to the public, would be of little use to schools. They would continue to take the usual precautions. The children's charity Barnardo's called the move "very bad news".
Labour MP Dan Norris, whose constituency in Wansdyke, north-east Somerset, will be the first area in the UK to test the scheme, said it was "an important blow in the fight against paedophiles".
The Home Office said it had not finalised the scheme and refused to confirm details. It said the main aim was to protect single mothers.
"Studies show the vast majority of child sex abuse involves family members and we are looking at ways of addressing this problem," said a spokesman.
The only information currently available to parents is figures on sex offenders resident by county. There is no separate information on paedophiles. In addition, head teachers are told about local "approved premises" if child sex offenders are housed there.