It isn't just about Maths skills. It can also affect the way you 'visualise' patterns. For example, I cannot sight read music. At all. I have to write the letters above the notes on both the music and piano and practise until I can 'hear' the tune. What I can do, is think logically.
Whilst some people will be able to just "see" Maths and can do chunking, skip steps etc. I have to follow logical patterns and stick to those. It is a struggle to adapt them without adapting the pattern and so forth. For example, I had to have a Maths tutor at 13 to learn how to tell the time with a clock hand and digitally. But I can now obviously!
For anyone who has this, I would advise that all that needs to happen, is to find alternative ways of achieving the same goal. Although I cannot sight read, I did get a pass at grade 8 piano with this approach. I scraped a C in intermediate GCSE 17 years ago, but now teach Computer Science and have also taught Year 7 Maths before. This is because I have found other methods of completing Maths problems by using 'steps' that my Maths teachers didn't tell me as Dyscalculia was a very very new concept back then (I was one of the first to be tested under the current 'test'). Explain a Maths equation by stating: "Do this, then do this etc." As long as I don't hit an exception, I can get the answer to the question. Just takes me longer than some others.
As the school teacher may not have enough time to explain every method to every problem in the hope your DC hits the one that they can do, I would consider a Maths tutor or arrange for one to one after school or lunchtime tuition. Failing that, use YouTube. There are a million and one videos for every problem - just a bit of research and your DC will find the method they "get" and can use in their lessons.