I have seen this in a few different places. And I couldn't take it anymore after reading it here again, so I have to add my few cents, it might be more than two.
Teach42 does a good job of at least looking for other reasons that students might skip class, but I'm not sure I've seen the obvious addressed: school sucks.
Why would any teenager want to be in that seat, unless you're forcing them to be? Are we, as teachers, educators, policy makers, giving teens a reason to come to school? And stay in school?
I must admit that even I throw around the term relevant like it was cheese on a pizza, but what does it mean for a HS kid who would rather spend his (or her) day lounging on someones sofa than in an uncomfortable desk, in an uncomfortable classroom, with awkward teenagers all around you? How do you make THAT situation relevant? Is it?
I say no. Rather, I say NO.
So...how do we fix that? Can we? yes. Yes!
1) what is it that kids NEED to know
2) what is it that kids WANT to know
3) how do those two things overlap
Teaching Pythagoreans theorem, while maybe nice to know, is NOT NECESSARY. I was never able to figure out how to actually use it, and to this day, have never actually used it. How to dissect pigs hearts may demonstrate important and transferable knowledge about our own health; dissecting sentences does not.
What are you teaching that you dread? What are you teaching that is totally and completely irrelevant? Most likely, if you hate it, so will your students. And once they wise up even just a little, and figure out that they don't HAVE to come to class after the age of 16, or whatever it might be in your state, they won't. Drop out rates--LOOK OUT!