Thank you for the responses. We can drop it here before this spirals out of control with the "should you or shouldn't you" debate.
Based on the overwhelming response of "I've done it with no issues with younger elementary-aged children" I plan on going through with it ... though the March 2019 trip will be flexible if things change - such as - my son is struggling, school testing is done that week, the school's policy is a bit more "firm" than I am interpreting, etc. We aren't flying, so I can cancel if need be (though my sister will be disappointed).
The fact of the matter is:
1) I care about my child's education - and I plan to make sure the school understands that.
2) I will do everything I can to limit the days off (to may be 4 days each trip) .. having more than a week, I feel, would be missing too much.
3) It's MY child, not the school's.
4) We value family time, and despite what value others (not on these boards) may put on a "Disney" vacation -- this is a huge part of that.
As much as I would prefer my son to be in a year-round schedule, where we can take several week long breaks throughout the year, he is not, So I am going to take him out of school (especially in these early years while I can) when it is convenient for the family (from a time and cost perspective - or in my case .. to be able to meet OTHER family). I am just a huge proponent of "go where the people aren't" .. so I don't like going on vacation when everyone else in the country is (aka - Summer, after Christmas, before Easter). (Though, admittingly, that is harder to do at WDW. .. heh)
I will make sure I will explain to my son that we are taking a planned family vacation .. just like daddy can take some time off of work, we are taking some time off of school and this is not "skipping" school. I want to instill in him it is important to go to school and you can't just not go because you don't "feel" like it.
Now time to look at booking a resort reservation for March!