Education bodies have underlined their support for assigning named persons to every child in Scotland, despite opponents of the scheme promising legal action.
The controversial plan to protect under-18s from harm is part of the children and young people bill backed by MSPs last week. But named persons - who in many cases will be a school leader - are widely opposed by parent and religious groups.
Supporters say that assigning state guardians will help to prevent child deaths by eliminating gaps between different children's services.
However, opponents fear that the move - due to come into force in 2016 - will interfere with family life. Scotland's biggest teaching union supports the idea but has raised concerns about the implications for schools.
"We agree with the principle of a named person to provide a single contact point to enhance children's access to services and support," said Larry Flanagan, general secretary of the EIS teaching union. "However, we are also very clear that this is not a cost-free policy and will have significant resource implications in cases where a school is expected to be the provider of the named person."
There could be "significant variations" in the level of support required by a child, so smaller schools should not always be expected to provide the named person, he said.
Ken Cunningham, general secretary of School Leaders Scotland, said: "Any legislation which ensures a child getting access to the right support is to be welcomed. The principle is therefore welcome.
But he added: "We hope sincerely that the government has done its homework and realises the serious resource challenge that remains, especially within secondary schools, so that named teachers have not just the legislative backing of a bill but also the time, skills, competencies, capabilities and knowledge to enable them to fulfil their new roles.
"There will need to be some clarity around how such named persons are selected and a whole suite of practical issues: for example, around the fairly frequent changes in staff, administration and record-keeping."
Scottish home education charity Schoolhouse objected to the scheme because it believed it would create "an obligation on the named person to interfere regardless of the wishes of the parent or child". The charity has written to the secretary of state for Scotland, Alistair Carmichael, requesting that he refer the legislation to the Privy Council.
Meanwhile, pressure group the Christian Institute said it would pursue a court challenge because named persons would "intrude" into family life.
The Scottish Conservatives unsuccessfully proposed amendments which would have meant that the named person would become involved only where there were concerns about a child's well-being or safety, and which would have made all 16- and 17-year-olds exempt.
"This will tip the balance of family responsibility away from parents towards the state - something which most parents find completely unacceptable," said party spokeswoman Liz Smith. "Forcing all young people to have a named person will, inevitably, dilute the resources available for our most vulnerable children."
Scottish Liberal Democrat leader Willie Rennie said that the arguments for the principle were backed by evidence but it was at risk of being "undermined by the government's inability to be clear about the resources allocated" and its "insistence on universal application for all 17- and 18-year-olds".
Children's minister Aileen Campbell said the wide-ranging bill would help Scotland to become "the best place in the world to grow up". She highlighted free school meals for all P1-3s from next January, strengthened legislation on school closures and 600 annual hours of funded childcare for three- and four-year-olds and the most vulnerable two-year- olds.
But Mr Flanagan said the government had missed an opportunity with the bill to ensure that children aged 3 and 4 had access to a nursery teacher.