Has anyone got any advice on the best way to do this, or can anyone reccomend any good publications that explain these conditions to a child.

I just told ds2 what the test were for. 12 yo's are pretty with it. He already knew there were things he couldn't do and being told he was being tested for a 'condition' made him feel better that he wasn't clumsy or stupid.
So if anyone remarks on his handwriting or laughs at him for not being able to catch a ball he can tell them he is dyspraxic (except MIL, cos all these new fangled conditions are the result of bad parenting and attention seeking of course) or know they are being wankers.

Thanks Riven, I was sort of hoping that would be how ds would react - i.e feel better knowing there was a reason behind his problems.
I have not considered telling any family yet, I think we would get the same response as you - it's all my fault for being a crap parent.
I will be forever grateful to the doctor we saw, who took the time to explain that nothing we did as parents would really have made any difference to our ds. I was not a bad parent, I had just been worn down by years of difficult behaviour that was not quite bad enough for me to believe it was sen. That kind doctor made me feel so much better about everything.

God, people who still think conditions such as this are due to bad parenting really need to climb out of their ignorance and read a book or two, or even surf the net for 5 mins, rather than regurgitate old, outdated and wrong-even-at-the-time opinions. The so-called "refrigerator mum" theory of autism was discredited almost the moment it was mooted back in the 50s, yet some people hold on to this old, ridiculous and damaging theory. Luckily no-one has ever paraded such ignorance in front of me, but I'd just tell them that autism and similar conditions are genetic, just like being born with blue eyes. If your parents are this rigid in their thoughts, and unable to open their minds, then tell them they're probably on the autistic spectrum too and that's where it's coming from (ok, that last bit's a joke but it does make my blood boil when people's ignorance makes life harder than it already is with an SEN child.) I have an ASD son and my husband also has an ASD daughter by his first marriage - it's pretty clear to me therefore that it's genetic as otherwise it's too much of a coincidence that he has had an ASD kid with two completely different women.
Ican'tfind - my 12 year old DSD was only told she was autistic about 2 years ago, and she is coping with it pretty well. I have just bought her a book on amazon about social problems in autism, but haven't read it yet so can't say if any good. My DSD told me she read "the curious incident of the dog that barked in the night" and that helped her understand autism. Good luck!

my MIL thinks I am making up ds1's aspergers and ds2's dyspraxia for 'attention'
FFS, I have dd2 with severe cerebral palsy and epilepsy to get all the attention I need!
And cos dd1 lives with her she's filled her head with this crap too. MIL was a physics teacher btw, not a neurologist. Oh, and I don't have MS either because its not exactly like her firned who had MS. I'll just leap up out of my wheelchair then and skip off down the road now she's sorted that out.
grumblegrumblegrumble

your MIL sounds like an ignorant judgemental old cow riven!! As if you didn't have enough to cope with!