It sounds to me as if he hasn’t mastered the pre requisites to more advanced concepts.
If you concentrate on the basics and he really gets to grips with the simple stuff he’ll catch up on the more complex parts.
Don’t worry so much about the current workload but look at fundamental numeracy.
Does he know the “story” of each number 1-10? The story of 4 is
0+1
1+3
2+2
3+1
4+0
Does he know that if he needs 4 forks to set the table and you give him 3, he needs to get 1 more?
Can he make dot patterns for 4?
For each number a child needs to grasp strongly the fourness of four etc with absolute certainty.
After that level:
Can he count in 2’s
In 10’s
In 5’s
Can he count in ten starting from anywhere eg 7,17,27,37
Does he know that 2+3 and 3+2 are the same sum?
If you say a number can he tell you one more and one less?
If all this is in place then I’d concentrate on learning tables. Dull but utterly essential to maths success.
There are loads of ways to practice- stamping, marching, playing trains, stacking, bouncing..,
Let him teach you if he’s resisting you teaching him. Teaching is just as effective a way of learning.
While you’re working with him break it into 3 parts :
Organisation skills- what do we need to do this task? Where can we find a pencil? What else do you need?
Working on the task
Feedback: praise first and find at least 4 things to praise. (You started without complaining/ you concentrated well/ your work is neat/ you made a great effort...)
Then ask him what needs improving (1 or 2 things)
Physical stuff:
If he’s sitting at a table make sure his feet are flat on the floor or on a box or step. This makes a massive difference to postural muscles and to things like concentration and hand writing.
If he hates colouring check his fine motor coordination. Is his handwriting neat? Can he keep between the lines? If not he may need to develop shoulder strength (crawling/ climbing/ baking/ washing windows/ digging/ painting walls up high/ pulling rope on a pulley, wheelbarrows).
Sorry to throw so much info at you in one chunk.