I'm a person that puts more merit on life lessons rather than 'book learning.' Going to WDW last month was my daughter's first family vacation that was longer than 2 days. My mother, daughter and I took two days to drive down, spend a few days at WDW, a couple days at Clearwater and than a couple days to drive back up.
Yes my daughter missed a week of school but I believe it was well worth it. Her teacher sent a note home saying that it was nice to see her back in class with a nice tan and that she was actually ahead of the class because they had reviewed while she was gone. And in all honesty, we didn't spend all that much time on her school work while on vacation. Probably a total of 6 hours but the family time, real life time and fun time was all worth it.
I think that as long as parents don't pull children out during 'critical' times (testing, lots of new material being presented) and are tuned into how well their child is doing, there is no problem with it.