A father who refused to pay a £120 fine for taking his daughter on an unauthorised term-time holiday has won a High Court ruling in his favour.
Magistrates had ruled that Jon Platt had no case to answer as, overall, his daughter had attended school regularly.
Isle of Wight Council had asked the High Court to clarify whether a seven-day absence amounted to a child failing to attend regularly.
The government says it will now consider making alterations to the law.
"We will look at the judgement in detail but are clear children's attendance is non-negotiable so we will now look to change the law," said a spokesman for the Department for Education.
"We also plan to strengthen statutory guidance to schools and local authorities."
Lord Justice Lloyd Jones and Mrs Justice Thirlwall dismissed the council's challenge, ruling that the magistrates had not "erred in law" when reaching their decision.
They ruled that the magistrates were entitled to take into account the "wider picture" of the child's attendance record outside of the dates she was absent during the holiday.
Outside court after the ruling, Mr Platt said: "I am obviously hugely relieved. I know there was an awful lot riding on this, not just for me but for hundreds of other parents.
"I think it's a very sensible judgement. It wasn't a complicated matter.
"Ultimately the arguments put forward on behalf of the Isle of Wight council amounted to, as the judge spelt out, if he was to believe and take it to its natural conclusion... a single day's absence from school amounted to a criminal offence.
"And no court was ever going to agree that that was what 'regularly' meant in terms of the Education Act."
Jonathan Bacon, leader of Isle of Wight Council, said he was disappointed the ruling had failed to clarify the definition of attending school "regularly".
Mr Bacon said government guidance had been that it meant attending every school day, but added: "Today's ruling may be taken to imply that parents can take children out of school on holiday for up to three weeks every year.
"This will clearly have a detrimental effect on the education of those children," he argued.
Labour's shadow education secretary Lucy Powell called the ruling the "worst of both worlds".
"All the evidence shows that regular attendance at school is an important part of ensuring that children fulfil their potential.
"This decision has been coming for a long time and the government has missed earlier opportunities to deal with it decisively," said Ms Powell.
Since 2013, tougher government regulations have meant head teachers can grant leave of absence to pupils during term time only in "exceptional circumstances".
According to local authority data, almost 64,000 fines were imposed for unauthorised absences between September 2013 and August 2014.
Many parents complain that the cost of going away in the school holidays can be four times as much as during term time - but the government says there is clear evidence "that every extra day of school missed can affect a pupil's chance of gaining good GCSEs, which has a lasting effect on their life chances".
Mr Platt, 44, took his daughter to Disney World in Florida in April 2015.
Her school, on the Isle of Wight, had refused permission for the trip but he took her anyway and she missed seven days of lessons.
Mr Platt was issued with a £60 fixed penalty fine.
After he missed the payment deadline, the council doubled the fine to £120 which he also refused to pay.
Isle of Wight Council then prosecuted him for failing to ensure that his daughter attended school regularly, contrary to section 444(1) of the Education Act 1996.
Mr Platt successfully argued there was no case to answer as the prosecution had failed to show that the child did not attend regularly.
Even with this and other absences, Mr Platt maintains her attendance remained above 90% - the threshold for persistent truancy defined by the Department for Education.
Mr Platt, originally from Northern Ireland, raised £2,300 in charitable donations towards his legal costs but says that now he has won he will donate the money to the NSPCC.
Craig Langman, chairman of the Parents Want a Say campaign against the term-time holiday ban in England, said the court case was "a pivotal moment".