ADHD vs. Depression in Children

I am a pre-k teacher and I have a student who I think has ADHD with depression,but I think his disorder is reflecting more of anger and distruction.He purposley goes "against the grain",he tries to hurt other students,distroy anything he can.I've tried everything to help calm him down but that just seems to set him off even more.His actions seem to come from nowhere,like a switch that goes off for any or no reason.Could this be an anger or no impulse control disorder?

I have a 14 year old son.  He came to me because he can't concentrate, he says he hears fine, but doesn't "hear what people say".  I often say things to him, he acknowledges that I've spoken, I'm ask for a response, and he says "what?"  I ask if he heard me he says yes but has no idea what I said.  He is frustrated with school, falling way behind.  He is in advanced classes because he tests great, but homework/study is too frustrating.  He says he can read it but doesn't "get it".  When we work on homework together, he gets frustrated and acts like he's gonna have a melt down. 

He says he needs to concentrate, he wants to understand things better, and wants to fix whatever is going on.  He is quite the opposite of hyperactive, he's very quiet and shy.  His doctor wants him to try ADHD medication and see how he does on it.  I read up and agreed that it his issues sound exactly like ADHD....After reading your post about the slow movement and speech and sleep issues, I am now leaning more towards depression & stress.  He can talk just fine sometimes, but sometimes it too low and muffled to understand, or I'm going deaf (which is his opinion),,,anyway He is overweight, high school next year, failing, bullies bug him. 

The dilemma is do I go to a new doctor, he's had the same one forever?  A psychiatrist?  Do the ADHD med for a while and see how it goes?  Don't stimulants make depression worse?  Someone it still may help with comprehension and his ability to pay attention and focus in addition to the appetite suppressant which would result in weight loss and possibly relieve some of his stress.....I'm going crazy myself trying to figure out the next step.

Suggestions would be appreciated.