When I was little (through middle school) my parents would pull me out every year. We travelled with my grandparents, and my uncle and his family to the Florida Keys to camp for a week, and then to Disney to camp and visit the parks for a week. We always drove, and the whole trip took about two weeks. My cousin and I would have daily homework to do, assigned by the teacher, and we had to do that each day while on vacation. Those times with my family are some of the best memories I have as a child.
We have never taken our kids (DS10, DD6) out of school for more than 2 days for anything before. As a teacher, I know that being in school is important, and it isn't easy (or in my mind responsible) for me to take time off during the year. In fact, in 20 years of teaching I have never taken a vacation during the school year. The most I have ever done is take two extra days around a weekend for a quick trip to the beach.
Our first trip to WDW with the kids was two summers ago (2014). It was hot, and the lines were long, but we figured that was the only time to go. We made it work, but we didn't enjoy the heat and humidity, and it really sapped our energy levels and enhanced our irritability.
Earlier this year, my wife suggested we go back during Spring Break 2016 to avoid the heat. I said that the two busiest weeks are Christmas and SB and that I had no intentions of going then, even if we did avoid the heat. But then it occurred to me, that my kids will only be young once, and that I will only get so many chances to take them to WDW before they get too cool to be seen with us. So, we decided to take them during January 2016, around the MLK holiday. They (and I) will miss four days of school, and we will have six days in the parks.
I would say that until high school, there is nothing that cannot be made up as far as schoolwork is concerned, as long as you pick a time away from exams, the beginning of the year (when kids are just getting their bearings), or during big projects or activities. I have had students leave the country to visit family all around the world for several weeks at a time. I would say it also depends a great deal on the student. Some kids can be out, handle the makeup work, and not miss a beat. For other kids, it can totally disrupt an entire marking period worth of learning. Only parents know their kid and how it may affect them.
For my wife and I, it is totally worth it. We haven't done it before, and may not ever do it again, but for us, it is about the time that we spend together as a family, and the decision to not play "by the rules" for once in our lives. We are both hopelessly type A, and doing this makes us anxious. But I am sure that the minute we get there, and from that point forward, we won't regret our decision.