This article: http://blogs.edweek.org/edweek/inside-school-research/2012/05/study_one_in_10_students_misse.html
Hits on one of my biggest frustrations this year. My students don't come to school. There are various reasons, medical, difficulty with transportation, insecure housing, family dynamics, but there are too many kids in my class who have missed many, many days.
If they are not here I can't teach them. It's as simple as that. Even when I am able to make the most of when they come to school it is difficult to carry on the momentum, pace, and repetition needed for academic mastery.
And there is virtually nothing we can do as a school. There is an attendance officer but he's busy with the high schoolers. We call daily, we talk to the parents, I've even gone to someone's house to pick him up, but it doesn't change the pattern.