When we go next month, it will be the third time we've taken our 11 yo ds out of school (this is our first trip to WDW, the others have been to DVC Hilton Head). He's now in 5th grade, other times he was in 3rd and 4th. We always go for a week (6 days this time), and I always feel guilty about doing it. BUT, he is a good student, and it has never hurt him. At HH, it's always my entire extended family (parents, siblings and their kids) and I think the time spent with family is more important than a few days of school. They will never forget these trips with their grandparents.
Our official school policy is that vacations are discouraged, and homework will not be given ahead of time. Sme of the teachers stick to this, some don't. This time we return 3 days before the end of a quarter, so I hope they'll give him some work ahead of time, or it will be a bear to finish it in time. We just decided if he gets lower grades this quarter, we know why, and it's still worth it. We will take some work with us, and see that he does as much as possible. I also have a kindergartener, but he'll make up his work easy enough.
IMO, bottom line is that while school is very important, family time is more so (and I had a teacher tell me that last year when I told her we would be gone, so that alleviated some of the guilt). If it were possible to go in the summer we would, but our business doesn't allow it.
Yes, I'm still a little nervous about telling the school we will be out, but I won't let them stop me.