It is good to see that you have taken an interest in this boy. As a Nutritional Psychologists I suggest that his mood disorders may be due directly to hypoglycemia, a nutritional disorder that can cause severe mood disorders among young children.
If he scores high it may be positive for hypoglycemia, which could be responsible for the symptoms. This can be treated by going on a hypoglycemic diet (Search our web site for this). Please discuss with a Nutritional Doctor, Clinical Nutritionist or a Nutritional Psychologist, if self-help therapy fails. Try to avoid drug therapy as much possible.
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I feel if you want to help him somehow he will need to get some nutritional treatment before you will be able to calm him down, or help is concentration and increase his attention span.
This is a big job but once you understand the principles of nutritional medicine and its influence on behaviour, you may be able to do something.
At least familiarise yourself with the connection between nutrition and behaviour and you will able to better understand how this boy can be helped.
I bet there may be a diabetic gene running in that family that may render that family rather dysfunctional.