Maybe I am an exception to the rule but I would just send in a note that says your child will be absent from X day to X day & you would appreciate if he/she could get their homework/make up assignments so they can be worked on during flight/ride to WDW. I might mention that the dates have been approved by the principal. I would also add any questions, please call me at #.
Here, my HS children have a vacation slip that gets filled out & signed by the student, parent & teachers as well as the principal and then it is the teachers responsibility to make sure the students have their work to take with them.
IMO, the school, teachers, principal doesn't need an opinion of what the student will learn while on the trip, just that you (the parent) are taking your child.
Either way, have a Magical trip. My children are also missing 8 days of school.