We have struggled with that same problem. Altho this past Dec was the first time my DS (10) has missed 3 days over us going to Disney. If we didn't check in by a certain date, our rate would have doubled & then we couldn't have gone at all. We told his teacher a month prior to our vacation & altho she couldn't give us work ahead of time (school policy), she did tell us that since our DS does well in school, not to worry. Once we returned, he had to catch up on those missed 3 days & it was no picnic but he did it (he gets one day to catch up for each missed day ~ so he had 3 days to turn in the 3 days he missed.) He did fine.
Now we have the opportunity to take a cruise with a dear friend who is a cast member, under her special rates & this cruise would be happening during the school year. We already spoke to his teacher about it (we don't know exactly when this tirp will happen since we can only cruise when there are several cabins still available) & her words exactly were "this is an opportunity that you should not miss. Sometimes a trip like this can be more educational than sitting in the classroom for a week."

Was quite surprised to have a teacher say that but in any case, even tho it is against school policy she would be willing to give my DS his tests ahead of time & some work ahead of time too (when this trip comes up.) We really appreciate her cooperating with us because once my friend leaves Disney, this opportunity to cruise for such a low fare would never come up again. This time he'd be missing one full week.
Let me make this perfectly clear, if my DS was struggling in school, there would be no way at all we'd ever consider taking him out for a week's vacation. No way. School is tough now. Not like when I went to school! But he's in the 4th grade & he's doing very well & his teacher even condoned him missing a week for this opportunity of a lifetime, so we're going for it (if & when this trip happens!) Oh & when he missed the 3 days of school for our December trip to Disney, teacher just asked that he turn in a little report about his Disney experience (the drive down, the weather, the parks, the food, etc....) He was only to happy to write one. He was so excited about it in fact, that he started writing about his trip in his autograph book! One more thing I'd like to add which will probably stir up the pot a bit.....if my DS's teacher were totally against him missing a week ~ we'd immediately cancel. We respect her & value her opinion. She sees him everyday in class & althou I see his papers when he gets home, I am not in school to see if much of a struggle went into him understanding what he's doing. Hope that made sense......