Have you had an contact with the school's SENCO (Special Educational Needs Coordinator) or has any been suggested?
If not asking for a meeting with them - see if they think there's anything amiss with him that might need investigating or if there is anything they can do for him.
They vary in how helpful they are - but it would be a good first step if you do thing there's an underlying issue.
Do not assume that he can do it for himself, but don't do it for him. Teach him explicitly what needs doing to be on time, bring the correct equipment, organise homework etc.
^^This.
I still ask mine what they have that day or next day - not becuase I'm really bothered but as a way of getting them to check right week - two week timetable - and what they need - it's not fall proof but it helps them think about it and check before they leave.
Also asking about homework - what they have when it's due - have bought them a weekly board to help them get used to organising it themselves but still asking so they work though when stuff is needed by.
Also trying to keep school stuff in one place - spent years searching for random items last minute so it's taken time to learn. Place to work quietly at home as well.
X-box and other things he gets after homework is done to a good standard - might mean checking it if he's got in habit of rushing it on buses.
talking , not focusing, messing with something around him
I think that's harder to deal with at home - is it paricular subjects or teachers or all of them? if some is it who he's sat by, the interest level in the subject? Does he have short term memory issues - can he follow multi step instructions - are sight tests up to date do you have any conerns about hearing?
You can focus on long term goals -see if he has some see you can use them to motivate him now - see if he needs to reach a certian level and lay down the basic expecation that you expect him to pay attention but as you are not in the room it does come down to him.