
We just went with our DS15 to the high school AP class info night last night. He's so excited about getting ahead for college, which is wonderful, but having just read this thread yesterday, all I kept thinking about was how can we take him out of school for WDW with a heavy courseload of AP classes?!

(Seriously, he has 9 AP classes he wants to take over the next two years before grad. Don't think he'll get them all in, but I do think a grad trip will be well deserved, don't you?)
When our kids were in elementary school, we took them out for a maximum of three consecutive days (for a
Disney Cruise) piggybacked around other scheduled days off for holidays or teacher conference days. Each time, we worked with the teachers in advance and got the work done. A couple times teachers just asked my kids to keep a journal and share stories upon their return, and accepted that as "alternative education."
They are now in middle/high school, and DD is in her junior year with lots of AP classes. She's getting a celebration grad trip, too...5 nights on the Dream in June 2011, though of course we all benefit
There's just too much work for the kids to make up right now, though, so
for the last three years, we have bit the bullet and paid the captive market inflated prices for Disney cruises during the summer months. Our 7 night cruise last summer on NCL to Alaska was actually pretty cheap compared to this coming July's 4 night Wonder. When you look at the costs of the same Disney cruises "off peak" you just have to cringe. We'll pay the price...for now.
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I know there's lots of debate on this topic. Like many others posters, I don't necessarily see the School Day as sacrosanct. There are plenty of days I know both my kids have done next to nothing at school due to standardized testing scheduling, major assemblies, etc. They watch movies, have bagel parties, etc. I don't see this as a big deal...as an adult, nearly every place I've ever worked has had its share of long buckle-down days as well as days when there was a team lunch or conference during which felt like I did no work. At school, some days the kids learn a lot, other days, not so much. I guess I see it as cumulative. As a former middle and high school teacher myself, I didn't kid myself into thinking my classroom was the only place my students could learn something valuable.
School districts are driven by desperation to cling to state aid...attendance is mostly about dollars. Punishing families who take their kids out of school by not letting them make up work would be tough in our district. We have large Indian and Mexican student populations who regularly return to India and Mexico for extended times during the school year with no apparent detriment on their grades or promotion.
So I guess the best thing is to consult your own Jiminy Cricket, and let your conscience be your guide!