Hi Mumteadumpty:
This may not work - but have you considered reviewing the concept his homework is based on before starting the homework.
So, for example, say he was working on probability problems but couldn't quite recall how to do it have you consdired typing in How to do probability on a search engine and seeing what you get?
BBC Bitesize KS3: www.bbc.co.uk/education/topics/zgf3cdm - often has simple explanations of topics covered which just help to review terminology & process. Sometimes there are games/ activities.
So I typed in 'How to work out probability KS3' - and got:
www.bbc.co.uk/bitesize/ks3/maths/handling_data/probability/revision/7/ - from BBC Bitesize
came across this useful slide show which sums up basic KS3 concepts - including probability: www.slideshare.net/torixD/preparing-for-ks3-probability-formulae-and-equations-ratio-and-proportion-percentages-of-quantities-and-fractions-of-quantities - I tend to bookmark stuff like this
Came across this teaching pack from Lancashire Grid for Learning (very reliable web page IME): www.lancsngfl.ac.uk/secondary/math/download/file/PDF/SB7%20Part%203%20Unit%207%20Probability.pdf
tried video options and got this:
I frequently use Corbett Maths videos - huge long list - just look up area you need help in and watch - corbettmaths.com/contents/ - this is what he had for probability - corbettmaths.com/2013/06/15/probability/
Sometimes watching a video - having the opporutnity to rewind (which you can't always do for your teacher) - can really help clarify the process and once that's clear the work is fairly straightforward.
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When you talk to the teacher - I think the thing I'd be interested to learn is whether there are gaps. i.e. he gets multiplication tables but is not applying that knowledge to fractions to create common demoninators when adding simple fractions 1/3 + 1/4.
It may be that he knows times tables but is shaky on inverse times table facts or can't apply that knowledge to more complicated problems like 236 x 89 or word problems.
If any of the above is the case - I suspect practice, familiarity with the concept and a bit of confidence as he improves will make a huge difference.
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Finally - I know that often kids get daunted because they fell everybody is 'getting it' lickity split whilst they're really having to think. Please reassure him there will be aspects of maths that will make them stop and think - the point is to recognise you're finding it tricky now and do something about it then so you can both keep up and move on. (I personally think persevering and working through a tricky patch in maths is a great life lesson and worth experiencing - gives you a lot of confidence to tackle something challenging in future).
HTH.