We have taken our DD ,now 9 in 4th grade, out of school every year to go to WDW. The only problem came when her 3rd grade teacher frowned upon it. At that time she only missed 3 days. I was told she would not be able to make up any work. Anyways, I requested a copy of my DD's math book and we reviewed on the plane and at night when we were just relaxing. When she got back to school she was very far ahead of her classmates in math.
This year she missed 5 days and her teacher told us to have a wonderful time. MY DH doesn't get much time of in the summer (this being the first summer in 20 years with the company). My DD did some reading on the plane and math also. When she got back to school her teacher gave her a history worksheet and she had an exam the following day. The teacher did not expect her to take the test but she did and got 100%.
I have my DD sign a contract stating that she is fully responsible for any and all homework missed when we return from vacation. She fully complies (the only time she listens to me!!), for she knows that we won't take her out of school in the future.
I am proud of her and she has learned so so much at WDW that a text book couldn't even compare. We still have her journal we wrote on our vacation fro Kindergarten. We tracked the weather and she let her classmates know that she travelled around the world in one day. It was and will always be a valuable learning experience.