ok, here's a couple of things you need to check if your son is doing the following...
* how many hours does he sleep at night?
* does he play video games? watch too much TV?
* is he fit and active?
* is he eating a well balance diet with enough fruits and vegs?
* has he got ADHD, ADD, dyslexia, dyspraxia?
as to increasing his concentration, there are research that fish oil high in omega 3 (EPA) will help. this is a long term intake of omega 3 and at a correct amount, at least 200mg for a 5 years old. thus, taking omega 3 is not going to make your son smarter and get grade A+, you still need to work with him to concentrate on his studies. i suggest you do further research/reading on this. here's one to start you off...
http://www.bupa.co.uk/health_informatio ... brain.html
DISCLAIMER: the information and advice contained in my post are intended as a general guide to healthy eating and are not specific to individuals or their particular circumstances. all content within this post is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. omega 3 is not a wonder food. you still need a healthy well balanced diet.