As a teacher, I would say that taking a high school student out is doing their academics a disservice, particularly if the school is on a block schedule (which is wonderful in many ways). It can be very difficult for the work to be made up at the level the student is used to. Most students do more poorly on makeup work than their usual standards, especially in math, which is what I teach. I would have strong reservations about taking a middle school student out of school for similar reasons. However, if an elementary age child is doing well in school, some time out for a trip is not a bad idea. I missed two weeks for family vacations in 1st, 2nd, 3rd, 4th, and 6th grade. We had the vacations in the summer after I got to a high enough level that the absences would have hurt.