I was also thinking like IC. Although a concussion can not help an already differently wired kid, it seems he had issues way before the concussion.
Is he seeing a psychiatrist (the guy with that MD) for a diagnosis and medications? They are the only professionals, besides NeuroPsychs, who can legally diagnose in the United States simply because they have a lot more training in a lot more areas. Therapists can not diagnose and do not have the scope of education to do so. And in my opinion no good pediatrician should listen to a plain therapist and/or parent and dole out any medication. That is not a pediatrician's field. My kids pediatrician would not diagnose anything that fell into the neurological/behavioral field. He would refer us to somebody who could, but said that a pediatrician is not really trained to do that right.
I prefer psychologists early on to plain therapists also and I've been a mental health patient since age 23 (I am 61). In the early stages of healing, you really need the best and brightest and most viable methods of therapy and most therapists are not "in the know" about that. For example, at this stage in my life and in healing, I do see a social worker because I don't need the depth of a psychologist. I learned about dialectal behavioral therapy on my own and asked her about it. She knew little about it, but is teaching herself. DBT is something any psychologist should know and it is extremely effective for many disorders that other methods don't help, such as borderline personality disorder. Just talking to a new patient is, in my opinion and experience, not enough to make them any better. If you have faulty thinking and out of control behavior, you need a different sort of therapy that teaches you how to both cope better and how to effectively change your thinking so that you don't get so angry and frustrated and don't act out. It won't work for everybody, and a lot of it is motivation, but I never thought that just talking about how I felt or my goofy family helped my depression or controlling my moods and anger. Cognitive Behavioral Therapy plus medication did tons and dialectal is helping on top of that.
Ok. Just my longwinded .02. Good luck 
