Well, since you posted to the AD/HD forum, I guess that you are wondering if he has this problem? Its possible - or not. But how to deal with the situation really depends on what is causing the problem. So its really important to find out what is going on.
Your first step is to get information on what ADHD or ADD is. The link at the top of this page - http://www.medhelp.org/medical-information/show/2157/Attention-deficit-hyperactivity-disorder-ADHD
is a good start. I can provide other good sources. Once you have an understanding of what AD/HD is - then the next step is to talk to your son's school counselor and ask for testing. If he is skipping classes, I would think that they will be interested in talking to you.
Another really good source of information (has a lot of info on schools and special ed, and testing, etc.) is "The ADD/ ADHD Answer book," by Susan Ashley. Hope this helps. Please post if you have other questions.