My 2 girls are both still in primary school.
We try to book holidays in the school holidays, but it is not always possible, due to restrictions when we can take our holidays, and also cost is a factor.
When we go to Disney this year, we are going over a school holiday, and the girls will miss 2 days at the end of the term to go early. The last week in school, they do hardly any work - they watch videos, have games and toy days when they take toys into school and play all day. If they are going to miss any school at all - they are the best days to miss!
As a family we love to ski, and it is very difficult to book a ski holiday without them missing school. We could go over Christmas and New year, but that is very expensive. They have a week off school in February, and we have gone that week in the past. It was nearly double the price, you can't get the child discounts, it is very hard to book, because all the teachers who ski have to book that week too, and when we were there it was so busy! We had long waits at the lifts, and the slopes were so crowded, we didn't feel very safe. The other week that is possible is around Easter, but depending when it falls, there may not be enough snow, and of course it is busy and expensive.
Luckily our headmaster is a keen skier, and has always allowed our girls to miss a week to go skiing. He told us that they learn far more in one week skiing than they do at school. It also helps that I speak French and German, and as we usually ski in France, Austria or Switzerland, I try and teach the girls more French or German, and they get to try it out in the country! They love it!