To summarise some of the above (and to add a bit more):
1. Scotland has a completely different education system to the rest of the UK, so their holiday dates have always differed greatly from those in England.
2. Holiday dates have traditionally been set by local education authorities, with each council area choosing their own dates. So there's always been a bit of variation in holiday dates across the country.
3. However nearly all secondary schools in the country, and a large number of primary schools, have now withdrawn from local authority control anyway and taken on 'academy' status'. That means that they're not obliged to follow local authority guidelines on holidays and are free to choose their own holiday patterns. (They have to ensure that their teachers attend for 195 days each year, and that their pupils attend for 190 days, but they're otherwise free to choose any term pattern they choose).
4. Some schools have now totally abandoned the traditional three-term school year, in favour of a six-term one where (other possibly than closing on public holidays) things like 'Easter holidays' no longer exist. That means that they have a shorter summer break but longer ones elsewhere (often at times when other schools in the area aren't on holiday). There are NO 'half-term' holidays but just six holiday periods (of roughly equal length) throughout the year. Norwich Free School provides a good example:
http://freeschoolnorwich.org.uk/onewebmedia/School%20Term%20Dates%202017%20to%202018%20(1).doc
5. Independent schools have never been obliged to follow a holiday pattern set externally and have always been free to choose their own dates. In some of the more affluent parts of Surrey, for example, over 90% of children attend independent schools.
6. The only way to be sure of the holiday dates which apply to a particular school is to look on their website (or to ask them directly).