Hey there...   Just to preface my answer...I am not a therapist or anything.  I am just a writer here on Health Central who suffers from depression.   I think this is a really good question.  It is hard to know whether it is true clinical depression when dealing with teens or whether it is just the normal sometimes moody behavior caused by both hormones and transitioning into a new developmental phase.    Here is a quiz about teen depression written by our Teri Robert here on Health Central.  This might get you started as far as finding out more about teen depression.  Christopher Lukas also has written a good article about teen depression which you can find here.   And I will just add my personal opinion about it.  If your son's eating and sleeping habits have changed drastically this can be a sign of a pending clinical depression.  Are his grades suffering?  Is he isolating himself?  Are there signs that he is suffering?  What would it be like to ask him directly if he is feeling depressed?   Truly though...only a skilled therapist can make the diagnosis of clinical depression.  If you are becoming more and more concerned...an appointment with the school counselor or a local mental health professional may be in order.    Thank you for your question.  I am sure a lot of parents out there are wondering the same thing about their teen children.