As DeniseM said, there are different rules, depending on your school district.
I realize most of the opinions expressed here relate to the American experience, but wanted to chime in with our Canadian experience, just for variety. Ten years ago, we took our 2 children out of school for 2 weeks in May for SIL's wedding in the Netherlands. We spent the first week in London, extended weekend in the Netherlands, and the rest of the trip in Paris. Our children experienced all manner of historical sites (Tower of London, Buckingham Palace, Stonehenge, Roman Baths, Eiffel Tower, the Louvre, Notre Dame, Sacre Coeur Basilica, the Rose Line in Saint Sulpice to name a few). Also, we were in the Netherlands for the 60th anniversary of VE Day - a historical event near and dear to both the Dutch and Canadians. Our children were in grades 6 (DS) and 3 (DD) at the time, and were able to spend two solid weeks in the company of their great-grandparents, grandmother, and extended family.
When planning the trip, I spoke to the school administration and teachers at the start of the school year. I asked about what the children would need to do to keep up with the work. Their response: keep a journal of the trip and present it to the class on return. The first-hand educational value of this kind of trip far outweighed the days they were scheduled to miss. Full disclosure: it didn't hurt that the 2 weeks we were away coincided with the prep time for standardized testing in the province.
During their high school years, we routinely took them both out of school for a week (4 days when coupled with a provincial holiday) for a mid-winter break. Both our children are now in university and doing very well. In high school, DS was on the Honour Roll and graduated with the highest mark in Geography (he would go on to major in this in university). In 2014, DD graduated from high school as Valedictorian, with the highest average of her class. We're very proud of both our children and we wouldn't have done things any differently with our vacations, given half the chance.
All of this to say: there are no hard-and-fast rules and what worked well in our situation, may not work (as well or at all) for others. We have incredible, priceless memories of our vacations, made even more poignant now, with great-grandfather gone.