Ladymuck:
Dyspraxia/ Dyscalcula/ Dyslexia are all spectrum order learning disabilities which can range from severe to mild and are hereditary - father to son, sometimes skipping a generation - and if both parents have gene, daughters can inheret. MIL who was a dyslexic therapist (now retired) said that usually when DD inherits dyslexia it will be toward the severe end.
Now there is no cure - this is a genetically inherited 'condition' which basically means you're wired differently from others. Interestingly at work we've been discussing whether it's 'throw-back' - as early man would not have required numeracy/ literacy skills and would have been a fairly awkward walker/ runner initially. They would have relied on quite literal recognition skills - that red berry with the funny white specks & five green leaves around the top (a wild strawberry) is safe to eat.
So down side - in today's world with lots of written text, lots of calculating, emphasis on athleticism - these conditions can be a hindrance - however they do mean that you have a highly original and creative way of thinking about things.
DH is severely dyslexic with a spelling age of a 7 year old, no ability to organise himself, no short-term memory whatsoever for conversations - BUT he has near perfect photographic recall. If he were foraging in the woods for survival of himself and his tribe, he'd be the one to follow about because he'd remember which plants are edible and spot them first. For work now, he uses that photographic memory but he was lucky enough to find a specialty that required it and colleagues that supported him developing this skill.
Now my advice is to raise this with the school and ask if he could be assessed - this is usually free and would help with school's frustrations (most likely) with his performance as well.
Diagnosis isn't a label - and as you rightly said there's no cure - but it is recognition of the condition and ultimately will allow for GCSE, AS & A-Level assessments to take this into consideration (i.e. extra 15 minutes for every hour of testing, someone to transcribe script, permission to type answers, etc....). This will also apply at University level.
In terms of remembering what to do - that is what an ink pen and the back of the hand were designed for. So have him get into the habit of writing PE Kit on the back of his hand (or whatever is important that day) - as his hand is very likely to be with him the entire day. He may be slow to remember to hand in homework first thing, but he will eventually look down and see the reminder.
Ultimately there will come a point where that writing on hand thing is embarrassing - that's when having a diary (or using a mobile phone diary/ note maker) could come in.
Finally - once diagnosed (if this is the condition) there is a lot of support for coping with the condition and developing strategies to function amongst all these 'normals'. However, please, please remember that the belief is that people with these conditions are working 1/3 again harder than us 'normals' - and therefore need down time to recharge those batteries.
HTH