Scottish families are still booking holidays at peak times during their own school holidays.
So?
@Oakandashsplash said "many do go on foreign holidays end of July before the majority break up"
Prices for those foreign holidays - or even UK holiday locations which are popular with both Scottish and English families (like Scotland itself, Cornwall, Wales, London) - obviously don't depend only on how many families of the same nationality are holidaying at the same time, but the total number of families. Certainly that applies to accommodation, but even for flights: since flights abroad from Scotland are rarely direct, they are in competition with English families for the 2nd leg of the flights
Scottish summer holidays run end-June to start-August - even earlier than English private school holidays.
So Scottish state school families will be competing only with 700,000 scottish state school children's families for those holidays, which will be even cheaper 1 week earlier.
Compared to English private school families competing with 600,000 English private school children's families + 700,000 scottish state school children's families - ie the families of 1.3million children - a week later.