home school child’s concentration

Hi Nicolene
I have an 8-year-old boy, who has a lot of trouble with school. He was in the private school, where we enroll our children, for his first two years. It became very apparent that he has learning difficulties, not able to absorb and remember what he is taught. For the first two years he cried every day or most days about going to school, He said he hated reading and writing lessons, because it was so hard and by the end of two years, he had made up his mind he would never be able to read and write. The next thing was he figured instead of looking hopeless in front of his teacher and pears, he would just not comply or try during those classes especially, but it spread to others as well because the level of achievement was widening in all areas of academic learning between him and the rest of the class. He started playing up in school and by 1/4 way through this year, the teacher could no longer handle him, or give him the special care he needs. We decided to take him out of the class, and He is now doing school with me in another room at the school along with two of my other school children, these two don't have a teacher so far this year, as they are very short of teachers at our school.
He basically does nothing unless I sit right beside him, normally with the threat of no play time unless he gets the work done, it is very easy work, more at a year one or two student level, he is a year three student. I need to spend time with the other two boys, and I have a baby, so that means he is nonproductive about 80% of the time and ends up playing. Then when I can give him my full attention, he takes a reasonable amount of effort to get back on task. I'm not worried about the playing if his work is done, but I'm struggling to find ways to inspire him to be diligent with his work even when mum can't help him and stop fighting about having to do it. He is in bad habits no doubt, and also has no real desire to learn, because he just doesn't absorb much, so he has very little interest.
Any ideas?