Jon Platt wins the right to take his children on holiday in term time. This is what that means for you

With a typical academic year involving 190 school days, the ruling suggests that 19 days of absence is acceptable

The Supreme Court is hearing evidence in a case that began with a disagreement over term-time holidays, then went to the Isle of Wight Magistrates and the High Court.

Last May, the High Court ruled that Jon Platt had no case to answer for refusing to pay a fine for taking his six-year-old daughter out of school for a family trip to Florida.

But why do flight and holiday prices soar outside school terms and what are the Supreme Court judges deciding? Simon Calder, travel correspondent and former maths teacher, answers your questions.

Q: How much do holiday costs increase outside term-time?

Package holiday prices typically rise by 50 to 100 per cent when schools are out. Increases in air fares tend to be more extreme, with some prices multiplying three or four-fold. A typical example for the February half-term: the morning flight on easyJet from Manchester to Geneva on Saturday 18 February for a family of four costs over £1,200. A week later, the price for the same seats on the same plane fall to less than £300.

Q: How can the travel industry justify such profiteering?

Like any sensible business, a travel firm will seek to maximise its earnings for the benefit of shareholders and staff. However, I don't see excess profits being made – indeed, most holiday companies are low-margin businesses.

Travel isn't like most industries. If an ice-cream maker detects high demand during a warm summer, it can produce more in response. But the supply of airline seats, hotel beds and rental cars, in the short term, is fixed. The average holiday firm or leisure airline trades at a loss for most of the year, but more than makes up for the shortfall when the schools are out. Most schools have similar holiday dates, and so demand surges when the school term ends.

Q: What does the law say?

Until 2013, head teachers in England were able to grant up to two weeks a year for family holidays in "special circumstances". But the then-Education Secretary Michael Gove, cracked down on parents taking children out of school during term-time, imposing fixed-penalty fines of £60 for unauthorised absences.

In response, a petition signed by more than 200,000 people asked the government to ban travel firms from increasing prices in line with demand: "It's time to stop the holiday companies cashing in on school holidays and let parents have some guilt-free family time! Enforce action that caps the percentage increase on holiday prices in school holidays".

But the consequence of any such law would be to reduce drastically the availability of travel, and there is no prospect of it happening.

Q: What is the Supreme Court deciding?

The event at the heart of the case involves Jon Platt, a 46-year-old company director from the Isle of Wight. He sought permission to take his daughter to Florida during term time. The head teacher refused. Mr Platt took her anyway. He was issued with a fixed penalty but refused to pay it. He was taken to court under the 1996 Education Act, but magistrates dismissed the case. The Isle of Wight Council sought clarification in the High Court, with the support of the Department for Education.

In the High Court, Lord Justice Lloyd Jones upheld the magistrates' view that Mr Platt's daughter's overall attendance record was satisfactory and he had no case to answer.

The judgment implies that parents need only demonstrate "regular attendance" of at least 90 per cent of school days. With a typical academic year involving 190 school days, the ruling suggests that 19 days of absence is acceptable – corresponding to almost four weeks.

The Supreme Court will rule on a narrow point of law: whether a child's overall attendance at school should be taken into account when deciding whether a parent has committed an offence by allowing their child to be off school. If the judges decide that it should not, parents will continue to be liable for £60 fixed penalties for unauthorised absences. But if they side with Mr Platt, they will endorse the principle that every child is entitled to be off school for 10 per cent of the academic year, whether off sick or on holiday. So if a child has had 100 per cent attendance up to the second half of the summer term, the family could legally take several weeks' holiday in June or early July, when prices are low.

Q: Why is the Department for Education so keen to fight the case?

The Government does not believe a parent's right to a cheap holiday in Florida transcend a school's right to expect regular attendance. If every parent decides to take advantage of the ruling by removing children for two or three weeks, classrooms could become chaotic.

The Department for Education says: "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," and will move quickly to change the law and "strengthen statutory guidance to schools and local authorities".

Q: Whose side are you on?

The teachers' side. Long ago and far away I used to be a maths teacher. I would not relish the prospect of explaining differential equations to a class of teenagers, then teaching the same lesson again a fortnight later when their pals return from Walt Disney World.

While I appreciate the benefits that travel can bring to a rounded education, my interpretation of the number of school-age British children I see in the theme parks of Florida in November is that they are not studying the complex interaction of potential energy, angular velocity and gravity – they are enjoying a cheap holiday.

There are plenty of work-arounds that parents can adopt. An alternative to that £1,200+ ski flight from Manchester to Geneva, for example, is a cheap £240-for-four hop from Manchester to Basel, from which trains are available to a wide range of ski locations.