Lawyers and teachers' unions had hoped that guidance published this week by the Government would clarify schools' responsibilities towards their students.
However, they say the advice is too vague and that families may use it to support a range of different legal attacks on schools, including bids for compensation in bullying cases, educational negligence claims, and appeals against exclusions.
Schools were given a legal duty to "safeguard and promote the welfare of children" under Section 175 of the Education Act 2002. The Department for Education and Skills says this duty goes beyond schools' existing responsibilities to protect children from abuse.
It also encompasses pupil health and safety, bullying, and meeting the needs of children with medical conditions. Other issues include providing first aid, school security, and tackling drugs and substance misuse, the guidance says.
Mark Blois, of solicitors Browne Jacobson, said the limits of responsibility remained unclear, so lawyers would use Section 175 to bolster compensation cases against schools.
The number of parents suing schools for failing to prevent bullying has fallen in recent years, but Mr Blois said he expected that the guidance could lead to a new wave of claims.
"It is going to be a stick that parents can use to hit schools," he said.
"It is not just the bullying claims. Lawyers could use it in cases where pupils sue their schools for failing to do enough to stop them playing truant."
The Secondary Heads Association said its members also feared a rise in compensation claims, which already cost schools around pound;200 million a year.
John Dunford, SHA's general secretary, said the legal duty was unnecessary because teachers already did their utmost to promote their pupils' welfare.
A DfES spokesman said that the duty had been introduced to protect pupils.
"It is not to make teachers liable to prosecution, disciplinary action or dismissal," he said.
Safeguarding Children In Education is at www.teachernet.gov.uk