I am not a professional, just a parent with a child on the autistic spectrum. I don't know the science behind it, but alot of parents have reported that their children's concentration is better using fish oil EPA and DHA. Infact there have been reported inprovements in concentration and it having a calming (de-stressing) effect on anyone, not just children on the spectrum or with ADHD. Whether it is useful in your case, you will really have to suck it and see. But try to go for a good quality product with EPA and DHA. There are also combinations of omega 3, 6, and 9 oils available. I think they need to be taken for a number of months before you see any improvement.
But this is also a non-invasive option to try and the omega oils are known to have health benefits.