Schools - not parents or magistrates - must decide whether pupils can be taken out of class for holidays in term-time, the High Court has ruled.
It is for schools to crack down on term-time holidays, say judges
Two senior judges said defying the school's wishes and taking unauthorised breaks could lead to court convictions.
The ruling follows an appeal by Bromley local education authority against a decision by magistrates to acquit a mother who took her girls out of class.
The mother had taken her three daughters on two unauthorised holidays.
The High Court judges said the magistrates had been misdirected to acquit her of the charge of being in breach of the 1996 Education Act for failing to secure the attendance of her children at their primary school in Bromley.
Lord Justice Auld, sitting with Mr Justice Sullivan, said the question was one of liability and whether the girls had "failed to attend school regularly".
It was plain in law that leave of absence "means leave granted by the school - not leave which magistrates consider might have been justified".
The mother of three, who cannot be named for legal reasons, was taken to court last year by her local authority in Bromley.
The authority was concerned about the girls' poor attendance between November 2003 and February 2004.
The mother had taken them out of school for a week's holiday in November 2004, which included participating in a dance finals competition, even though permission had been refused by the school.
The mother believed the competition to be "important for their development".
She then won a holiday competition in January 2005, resulting in further unauthorised absences, the judge said.
At a hearing last September, the magistrates found that the mother had not failed to secure her girls' regular school attendance.
Acquitting her, they decided she ought to have exercised more care regarding absences for holidays during school term - but the absences, in their view, were "justified".
The high court judges have now ordered the case to be sent back to the magistrates with a direction to convict the mother.
But there should also be a direction to give her an absolute discharge in view of the amount of time which had elapsed since the case was first heard, they added.
Every Lesson Counts
The government is keen to curb unauthorised term-time absences and wants to reduce current estimates that one in six truants on a given day is away with their parents on a family holiday.
Ministers hope a new scheme, Every Lesson Counts, will stop families in England going on holiday during term-time.
The initiative, organised by the Department for Education and Skills and the Association of British Travel Agents, offers discounts, free child places and early booking deals for families.