I'm making a separate answer here because after reading your question and your comments, quite frankly I'm scared for him.

Here are some things every parent should know about mental health that I had to find out the hard way (and almost lost a child in the process):

 - **Shame is a killer.** It will keep either or both you and your kid from admitting they need help until it is too late if you aren't careful.

 - Mental health issues tend to show up with puberty (7th grade would be a perfect time)
 - Boys are more likely to exhibit emotional issues violently. Perhaps this is psychological, or perhaps it is because society tells males the only emotion they are allowed to express is anger.
 - Persistent mental health issues (eg: ADHD, bipolar, chronic depression, or chronic panic) are quite likely to rooted in brain chemistry. You cannot reason your way out of them, or "tough" your way through them.
 - Everyone's brain is different. Some of us can make ours work within "normal parameters fairly well, some of us need help.

Fortunately here in the US medical coverage is (for now) required to cover mental health. So help should be available without having to make a Sophie's choice between financial solvency and your child's life. 

In my case my oldest really had a hard time mentally getting over the hump that needing this kind of help makes him "crazy". I mean a *seriously* hard time. 

I can't diagnose someone else's kid, but I could easily see there existing a boy that age whose shame at having mental issues is feeding into anger, which essentially randomly boils over, particularly with the people who were responsible for getting him to that point (his parents). But also some people (particularly bipolars) will just unload on the next person who thwarts them in some trivial way when its "time" for an episode. 

Straightening out what exactly it is, and what (if any) medication will help, is the job of a registered psychiatrist. That needs to be done ASAP.