The Supreme Court has reserved judgment on a landmark legal battle between education chiefs and a father who took his daughter on holiday in term-time without her headteacher's permission.
A local authority, backed by the Education Secretary, argued that a child's unauthorised absence from school "for even a single day, or even half a day" can amount to a criminal offence.
A QC for the father, 46-year-old Jon Platt, described the submission as a new and radical interpretation of the law which was absurd and would "criminalise parents on an unprecedented scale".
The clash came as Isle of Wight Council appealed to the highest court in the land against a High Court ruling in May last year clearing Mr Platt of failing to ensure his daughter attended school regularly, as required by section 444(1) of the Education Act 1996.
The council prosecuted Mr Platt after he refused to pay a £120 penalty imposed by the council for taking his daughter on a seven-day family trip to Disney World in Florida in April 2015.
Local magistrates found there was no case to answer, and the council took its case to the High Court in London.
But two judges, Lord Justice Lloyd Jones and Mrs Justice Thirlwall, upheld the magistrates' decision and declared in May last year that Mr Platt was not acting unlawfully because his daughter had a good overall attendance record of over 90%.
The decision caused a surge in term-time bookings all over England.
In a case being watched by parents all over the country, the council is asking five Supreme Court justices to overturn the High Court decision, saying it raises important issues over what constitutes "regular attendance" at school.
Martin Chamberlain QC, for the council, argued that all pupils had to be in school "at all times when required and in accordance with the rules".
He said: "Absence for even a single day, or even half a day, would constitute an offence."
Referring to Mr Platt's Florida holiday, he said: "Absence for seven consecutive days cannot on any view be regular attendance."
James Eadie QC, appearing for the Education Secretary, argued it would be "absurd" if parents could go on holiday with children when "the sun is out and foreign climes beckon" in a way that "undermined" Government policy on unauthorised absences.
Mr Eadie said: "Absence from school can adversely affect a child's educational attainment.
"Research indicates that every extra day missed is associated with a lower attainment outcome."
He added that it also disrupted the education of other children and placed an extra burden on teachers who had to ensure absent pupils caught up on what they had missed.
Mr Eadie said: "Undermining the authority of the school and head teacher and those responsible for running the school is likely to be a thoroughly bad thing."
Clive Sheldon QC, appearing for Mr Platt, argued it was the education authorities who were being absurd.
He said they were putting forward a new and radical interpretation of the law and the effect would be to "criminalise parents on an unprecedented scale" if their children missed school for various reasons.
He said there were 4.1 million days of unauthorised absence from state-funded schools in the 2015 autumn term.
On the local council and the Government's argument, that meant "there were 4.1 million criminal offences committed during one term".
Mr Sheldon said: "If the Government wishes to change the law and criminalise each day's unauthorised absence, then what it ought to do... is to introduce fresh legislation to this effect."
At the end of the hearing Mr Platt said he was "shell-shocked" by the Government argument, which seemed to be suggesting that "even a minute's lateness" to class was enough to amount to a criminal offence.
He said after the day-long hearing: "It is shocking that the Government did not back away from that position.
"It is now in the hands of the Supreme Court justices. I have great confidence in the British judicial system, but at the end of a tough day in court I have absolutely no idea what they will decide."
The court president Lord Neuberger said it would give its judgment "in due course".
Controversy was triggered when the Government ordered a crackdown on school absences in 2013.
New guidelines were introduced for English schools which only allow heads to permit pupils to miss classes in "exceptional circumstances".
Families complain that trips in official holiday periods are up to four times more expensive, and local councils have reported that the number of breaks in term time is increasing.