Thank you, that's all really helpful. I will have a look at that website.
I have gone around in circles over the years as to what his issues actually are! I would say:
He knows his times tables but we have to keep practising - he's like a leaky bucket.
He works really slowly - a combination of being a bit dreamy, slow reading or processing speed and just not caring about getting it done.
He is much stronger verbally than on paper - I think he often feels that he doesn't fully get his ideas across.
He just doesn't care! He will do the minimum and although he has been kept in to finish work, it doesn't make the slightest bit of difference for the next time.
Having said this, when he wants to do something, he is like a dog with a bone and can make a really decent job of it, IF you can get him interested.
I have often thought of just leaving him to it rather than sitting on him to get anything done, but I don't think he would rise to the challenge at the moment, and the risk feels too big. His teacher is really positive and seems to understand him well, and he likes her.