I think you need to find out what the cause of his behaviour is. There is a possibility that he is just a waster and a lazy bum who can't be fagged to go, but it is more likely that there has been a catalyst which has caused this particularly if he went to school willingly before.
I would talk to your gp and get him to see one too. He may be suffering adolescent depression, or he may be ill: glandular fever, diabetes etc etc. maybe he just feels he has no motivation or purpose whereupon, does he have to be in school? has he finished his exams? Would he be better off in employment and finishing his exams at adult ed?
talk to him, and get him to the GPs for a medical. It could be as simple as he's had a massive growth spurt and is just knackered. We all know how our toddler's behave when they are having a growth spurt - they sleep and whinge for days; I think we underestimate sometimes, the physical toll puberty takes on our teenagers and they get fed up too.
DOn't despair though, keep your cool and try not to nag. Teenage boys are like mini men: They need to feel as though they have arrived at a conclusion...you need to suggest and create the impression that they thought of it first....whatever you do don't nag. SOmetimes, men/boys behave badly simply for attention too. As they get older, they just have 'colds' and 'bugs' and get attention that way. maybe he needs some TLC.
hope you sort it. And as Lonnie says; post it in parenting and you'll get a wealth of advice from people who have got the tee shirt.