Families are paying over £1,000 more for a break during the school holidays than during term time, figures suggest.
A new report reveals the soaring cost of taking a family trip during the six-week break, with prices around 50% high during this peak period, compared with just a few weeks earlier.
Travel experts suggested that allowing schools to set their own term dates is a "good first step" to reducing sharp price hikes, but this needs to be coordinated to allow demand to be spread over a longer period.
The findings come on the day the Supreme Court ruled against a father who took his daughter out of lessons for a term-time holiday to Disney World, Florida, in April 2015.
An analysis by FairFX found that the average price for a package holiday for a family of four goes up by £1,310 if they travel in August, compared with travelling in June - a hike of around 55%.
And the same family of four would pay around £905 more - a 32% increase - to travel in August compared with four weeks earlier at the start of July.
The figures are based on an analysis of the cost of 104 packages holidays, travelling on August 5, compared with four weeks earlier and eight weeks earlier.
FairFX chief Ian Strafford-Taylor said: "Despite national outcry and a legal battle reaching the Supreme Court, the industry has ignored the plight families are facing up and down the country who are worried about the escalating cost of their holiday.
"Families accept they're likely to pay more to travel within peak holiday times but some of the price hikes we're seeing are outrageous and bring the industry into disrepute.
"There's an obvious supply and demand mechanic behind pricing strategies but with the cost of holidays being hiked so incredulously, it's not fair on families and these extreme cases need addressing.
"No parent should feel that they have no other option than to take their child out of school."
Travel association ABTA said that prices rise during school holidays and other busy periods due to supply and demand.
"More people in the UK and across Europe want to take holidays in July and August, at Easter and at Christmas, therefore prices rise during these times, as there is increased demand for a limited number of hotel rooms and flight seats," an ABTA spokesman said.
"Allowing schools to set their own holiday dates is a good first step to alleviating the sharp peaks in pricing.
"However, if it is to achieve results there needs to be a coordinated approach to staggering holiday dates to allow demand to be spread over a longer period and avoid any problems for families with children in different schools.
"While staggering holiday dates will help alleviate sharp peaks, demand, both from families and from consumers across Europe will likely still be concentrated around the traditional school holiday periods and so prices will still be higher at Christmas, Easter and in the summer, than at off-peak times."
The best way for families to get an affordable holiday is to book early, and to be flexible with their requirements, he added.