Hi idontunderstand
I think LittleMissGreen and Galena raise some good points but before you go back to the teacher - why not ask your son about what he's finding difficult in maths and when he asks questions.
Just looking at the situation structurally (and I don't quite understand what year your DC is in) - as this is a mixed class (maybe with Y6 and Y5 pupils) - it may be that your DC is not doing as well as the majority and possibly taking up a lot of teacher time.
So questions to consider:
Does your DC solidly know 12 times table facts?
Does your DC cope well with things like multiplication of two digit or three
digit numbers?
Does your DC cope well with division of two digit or three digit numbers?
Can he cope with dividing or multiplying by 2 digit numbers?
Does he get dividing with remainders? does he get expressing the remainder as a fraction or a decimal number?
Does he struggle with concepts like opposite angles - calculating values of missing angles (in triangles/ circles/ semi-circles)?
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If I were you - watch him as he does maths homework (if you have any) and observe how he's coping with it. It may reveal what the problem is and where your DC may need more explanation or practise.
Lots of great practice on Woodland Junior School Maths Zone: resources.woodlands-junior.kent.sch.uk/maths/ & if your school subscribes to an on-line maths website - you will find games & more to do there.
HTH