our first trip the kids missed 10 days of school, but that was the exception to the rule, we were to go over the summer, then my son was stillborn and we just couldn't muster up the courage to leave the house so soon, so we talked to our school superintendant and he approved our vacation and didn't allow the teacher to send too much work along. (granted DS was only in 2nd grade).
the past 2 trips were 6 days, this upcoming trip it will be 4 days because we planned it to leave on thanksgiving and took advantage of deer day.