I think it would all depend which grade in Middle School, what activities your child is in, etc...
My kids did choir -- being there for their choir concerts is part of the deal of being in choir. I think the teacher would be not very happy if I pulled them during a week the choir concert was planned for. My daugther was also in orchestra besides choir, so we had those concerts too.
Then there is state testing, so you don't want to pull them for that. Especially in 8th grade when those test scores determine which classes they will get in for High School.
My kids both did the 6th grade play, that's early in the year but no way could I have pulled them out if they were participating in the play.
My DD was on the cheer squad, so basketball season was out. This year my son is on the wrestling team, so that season would be out.
That's all beyond the work they would have to make up, which if the one week my son was sick in 2nd grade is any indication -- it would be a HUGE amount of work.
My DD last year was out for 7 weeks even with homebound tutoring, got behind in Math & forget her French! She never did get caught up with that.
There are *so* many variables when a good time is. I know our school takes the week of Thanksgiving off. I know there are several short weeks you could make it work but that would depend on your school district. I know we have 1/2 day Thursday, all day Friday & all day Monday type of weeks. If I were to pull them, that would be the kind of week I would attempt to use. I believe Columbus day is one of those, then January MLK day is one, I know we have one in Feb. (President's day?) as that is when the choir is doing their trip, so the kids only have to miss 1/2 day of school.
I know it's possible for it to be done but your kids may not be happy with what they have to do to try and recover from it. I know I've read on here before where after the kids have done it once, ask not to be pulled out again. It's just an individual thing.
I would just try to look at the school calendar & find out when there are some long weekends in there & use that as the starting point. I know we get our next school calendars out at least by February, so have some time to plan (if your school district works the same way). I know the 2010-2011 school calendar is on the next board meeting's agenda. We should be knowing what it is probably by this December.