What is his learning style? Is he a physical (kinaesthetic) learner?
Many children (especially boys, IME) are like this - they respond well to being able to manipulate things with their hands, rather than just being told something or looking at it on the board or in a book.
If this sounds like your DS, you need to find ways of physically representing the maths he's doing. Sounds simple but it makes a massive difference for some children, and often schools (again this is just IME) don't seem to cater for this learning style enough especially after EYFS.
Just really simple things like actually having objects to count, add, divide etc. Smarties are great for this of course :o
I've seen a great representation of negative numbers using little piles of soil/little dug out holes in the garden!
Cuisenaire rods are great, as is Numicon, because each number has its own shape and it's easy to see the relationship between them.
Other things that could help are things like cooking/weighing/measuring, playing with water (capacity etc), threading beads with patterns etc - lots of things that don't seem like maths, but will actually be cementing the concepts for him.
You could also get some magnetic numbers and play with them, put them in order, use them as a number line for adding etc.
I really like this article
this book is supposed to be good, and I really like this one for some fun ideas.
Sorry for waffling, maths is a passion of mine :o
HTH!