There are many school systems where missing a week would be very detrimental to a student's progress, it just varies from location to location sadly.
And from week to week. For example, our December trip involved the kids missing the last 4 days of school before Christmas break - a time when elementary schoolers are generally to excited/distracted to learn as much as in a normal week and when they're about to be out of the classroom and scholastic habits for two weeks so teachers adjust and present little/no new material. Our January trips have been in the short week created by end-of-semester (3 half days and a teacher inservice day), again, a time when little gets done in class aside from "housekeeping" type duties. Our middle schooler arranged to take his finals early and both kids missed very little.
That's why I suggested Sept to the OP. While it is an important time as far as social interactions, if they aren't changing schools the kids are likely familair with those expectations, and much of the material will be review that can be made up far more easily by parents than work assigned in the heart of the school year. In my state, testing is in October so those first few weeks of school are among the easiest to make up - they're reviewing material learned in the previous school year and brushing up on test-taking strategies, not moving ahead with new content.
I know that no one on this thread will agree, but taking one's child out of school for an extended trip to Disney World is hardly necessary when there are 13 or more weeks of school vacation every year. The OP actually said that he/she was just considering this to avoid crowds. My husband and I are both teachers, so our Disney time is usually during these vacations. Really, the crowds aren't so bad that they justify missing a week or more of school.
That's fine when you're a teacher or in another profession that can easily take off during school breaks, but the world doesn't shut down over the holidays or summer and a lot of people can't vacation at the times the kids are out of school. Those are the most desirable times to put in for vacation time and it often takes a good deal of seniority to get requests for the popular weeks approved. And many jobs are by their nature seasonal; when you can't work during the winter because of the weather, taking time off in the summer isn't looked upon too highly for anything short of a true emergency.
I definitely cannot disagree with this! I am embarrassed that I misread your previous post, but I know I didn't misread the other posts on this thread that were definitely anti-teacher/school...
I think it is very important to separate anti-teacher and anti-school. I'm not anti-teacher. The teachers I've known, both in our family and in the kids' school experiences, have been dedicated, caring professionals trying to do their best with what they're given. I am sometimes anti-school when it comes to draconian or inappropriate policies, but teachers don't set those policies. Administrators, most of whom have never been classroom teachers, do. And often they're acting based on concerns that have nothing to do with educational efficacy - funding, AYP, school rankings, and political forces are sometimes at least as important as educational priorities, sometimes moreso.