I wonder what proportion of holidays taken in term time are for life changing experiences like this, and what proportion are simply cheaper versions of the same all inclusive holiday in the Med they'd have taken anyway? Frankyl its like the sort of trips you'd do would be officially sanctioned by the head anyway.
The other reason, of course, that holidays cost more in the school holidays is not purely because it's the school holidays but because it's summer, which is peak holiday time even for those without kids. Look at the way air fares are structured - for most scheduled flights a departure date later than 21st June is peak season and significantly more money, even though it's not school holidays.
It comes down to supply and demand - there are a finite number of hotels and seats on planes, and the more people who want to purchase them the more they'll pay and the higher the price of these. Travel firms exist for one reason and one reason only - to maximise shareholder value. They charge what people will pay and who can blame them?