Get the facts, if possible, but don't browbeat or nag, but try to find out what's in your kid's head. Use open-ended comments such as "Tell me more..." or "I need more information..."
Tip: If talking with your teen is difficult and likely to end in an argument, make an appointment to see a counselor or other objective adult that both of you trust. See EduGuide Goal "Get Connected to a MS/HS Professional I Can Trust."