So... your teen won't go to school. First things first, you need to know that this is abnormal behavior. Teens generally thrive on social interaction... in other words, they live for their friends. So having a teen adamantly refuse to go to school, where they can see their friends, tends to raise a lot of red flags.
Whenever I see a teen who won't go to school, a few issues come to mind before all others. First, is the teen being bullied? Teens will often seek to avoid school to avoid a bully who has threatened them in some way. Next, does the teen have significant anxiety? If so, it's likely this anxiety is being triggered by peers, school pressure, or an embarrassing situation. Being involved in an embarrassing situation can be a powerful motivator for school avoidance. Lastly, has the teen been hurt romantically? Romantic entanglements and rejection can serve to fuel the internal feelings of inadequacy and ineptitude that often go hand in hand with adolescence.
Many times teens, especially males, will make every attempt to hide being bullied from their parents. This is especially true of their fathers. Male teens don't want their fathers to see them as weak or scared. Unfortunately, if the male teen perceives their father to be exceptionally masculine, this may lend itself to a more closed-lipped teen where bullying is involved. It's important for fathers, where this situation may be occurring, to be open and honest with their teens about their own fears, their own insecurities, and their own youthful struggles to be confident and brave. After all, we've all been there.
Next, school avoidance may be fueled by anxiety. Or more specifically, an anxiety disorder. Generalized anxiety, social phobia, panic disorder, and other anxiety-related conditions can definitely impact school performance and the willingness to go to school. If the anxiety is severe enough, teens can experience significant somatic symptoms associated with their anxiety. These include: stomach upset; diarrhea; headaches; vomiting; panic attacks; and others. The core of teen anxiety usually centers around a fear of embarrassment in front of peers. This is, of course, the most prominent symptom in social phobia. Teens, however, are more likely to exhibit this symptom even if they don't meet full diagnostic criteria for social phobia due to their natural and developmental focus on social relationships. If you suspect your teen may be experiencing anxiety, make an appointment with a therapist who can help you ferret out these issues.
Now, it's also possible that your teen has experienced a personally embarrassing situation or been rejected by a romantic interest. Teens tend to feel things deeply and question their own self-worth as a result. A romantic rejection can feel like a complete condemnation of who the teen is, and who they believe themselves to be. It often takes months for a teen to rebound from a romantic rejection. These rejections may, of course, be exacerbated by anxiety and/or embarrassing or public revelations regarding a rejection.
So... to be clear, this is not an exhaustive list of possibilities as to why your teen may be avoiding school. But, in my experience, these problems are the most likely suspects. The bottom line is this, refusing to go to school is almost always an indicator that something serious is going on... and the best thing you can do in this situation is to get your teen in to see a therapist. Not just any therapist though... one who can readily gain the trust and confidence of your teen. Getting to the root of the problem is going to be paramount to solving the teen's desire to avoid school.