Well, I have a 7 year old who I'm (sort of) training to think for himself.
I married my DH last year and thus became a Mum to a child who day dreams, never puts anything away, will often tell you he can't find things (because they weren't in the correct spot-1cm out and he won't see it) and unfortunately, I am organised, methodical and thus very frustrated by it. His father is a bit like this in the day dream sense but is organised around the house. His mother apparently was also a day dreamer who didn't like mundane things like housework or paying bills so my DH did all of this (my DH is a widower). The other (and possibly fatal) flaw is they'd been living with his grandparents who over spoilt him, did everything for him and if he broke something would tell him it's ok he didn't mean it (he broke a wedding present 2 weeks after the wedding and didn't even say sorry as he has been trained not to feel guilt).
So, I became nasty or rather slightly pushy Mum. We started with 'you must put your bag and shoes in your room when we get home' which took a little while, then we got onto 'if your toy is in the middle of the floor and I fall over it I won't be happy' and moved onto manners. It's not been helped as he still spends a lot of time at his grandparents but, after a big talk (after a parents evening where we found out he spends half a lesson day dreaming before starting work), at our last parents evening the teachers asked what we'd done to him as he's improved so much! His reading and maths have improved more than they should in a year in six months, just due to his concentration being better!
Saying all of this, we still have problems so, we have a new (less nagging) system in our house. If he does something extra good or helpful, especially without being asked, he gets a piece of pasta (eg. the other week in a helpful mood he re-arranged the throw and cushions on our sofa). If he leaves things in a silly place because he's being lazy or is rude/bad mannered or is naughty, he has a piece of pasta taken away. Twenty pieces and he gets a magazine. It's been a great incentive although now he's trying to do things to get pasta which is quite funny but not the point!
So, it is possible to retrain them, but expect it not to be easy and be firm.
Good luck!