Child with a bad memory.

Can anybody help?
My 10 year old son has an unusually bad memory, and his teachers are now saying that it is affecting his marks because he forgets equipment, forgets to hand things in (even when he put a lot of effort into doing them well), and can't remember what he has been asked. When he copies from the board he can't remember more than a couple of words at a time, so it is a lot slower.
He is the same at home.
He is also takes forever to do anything, and forgets what he's doing several times during the process.
Everything has to be planned down to the smallest detail, to the point where his time is up before he has even started. He's the same at home with games he makes up too.
Other than that his behaviour is as close to perfect as I could hope for, he is a good learner, is in a class for academically gifted kids (the school's decision), and is an all round lovely, caring kid.
He has noticed the memory problem himself, and it's really starting to upset him.
Does anyone know what could be causing it or how I can help him? I'm starting to get worried.