My friend uses fish oil for kids. You can buy it from any chemist.

My daughter is quite active and would rather run around and play when she first started school and couldn't sit and concentrate and needed one on one assistance to complete tasks a lot of it was settling in maturity and not understanding and having the confidence I think the teachers can get so caught up in telling them off for disrupting the class they forget that they are usually doing it for a reason and should be offering them more help.

We were told at the end of the year she needed to repeat but we turned it round by extending her home work alot and on the weekends Lots of one on one at home my daughter now in year one sits and completes takes in her class room on her own and has gone up four levels in reading keep talking to the teacher for updates as well and have appointments for a good talk to see how they are going how they are helping and what you can do to help.

My daughter also has four days a week help at school for around forty minutes during school time I also keep in touch with that teacher to because they do alot of testing.

Basically find out what they are struggling with at school and even when they are improving keep going its so easy for them to fall back into bad habits.

Some ideas to help when they read their reader offer an extra reader buy some of your own because repetition helps concentration and confidence, write sentences together using their sight words or spelling words buy some extra work books from your supermarket the school zone ones always go over the things you have learnt as well as introducing new things. (Read my Advice on Homework from school tips and early learning)

We do forty five to an hour homework each night on the weekend an hour and a half. She usually take ten minutes to focus but most days now five minutes the more you do the more they concentrate we cover reading three readers,reading sight words and they get a tick so many times then a sticker,our school zone work books (Beginning Reading,Maths Basic 2), do this with them explaining it very slow and letting them read some of it to.We usually finish with a game learning related. Basically any extended homework you do starting with their school home work will help them with their attention span everyday its a good idea to tell your child this is what we will be doing yes they complain but its now part of her day the occasional day off is okay if you have a play date but even that makes them negative about school work the next night so persistence is the key. 

Lots of praise well done and have a laugh to. Good luck let us know how you go the teachers at my daughters school cant belive how well she is doing now and they just dont get enough one on one at school we have to really step in trust me it works.

You may like to look at activities that encourage concentration and listening... maybe reading books and getting an appropriate reward (star chart etc) for remembering certain important information about the story. Another is sporting activities that incorporate complex (but fun) instructions. You may also find that it's just a matter of encouraging him to find ways to make the content he is listening to interesting. You may also want to have his hearing checked, eyes checked (I always remind my 4 year old son if he can't concentrate or is bored to look and watch the persons lips whilst talking) I have just learnt that I play tennis better by just watching the ball and not think of anything else. This may work also for listening to watch the mouth of the talker.

Also, it may take time to get familiar with the classroom surroundings, smells, sounds and he may just be getting used to new people, new routines, new demands and all in just one room. I would see how he feels about what he is experiencing and if you are worried to talk about it with your doctor just to rule out anything extraordinary or if anything drastically alarms you. You may also want to talk to the teacher, they often will give you an indication that it's just time to mature or if your son is really struggling (which is very common)

Here's a search in Minti on some awesome advice right from parents who have dealt with the very problems you are experiencing and you can seek advice direct, hope it helps

http://www.minti.com/search/?query=concetration+span&item_type=advice&x=0&y=0