You can try making him write using crayons or sketch pens of different colours, use attractive writing material, practice writing with him, and give him a lot of practice frequently. Also, for spellings, since he complains of forgetting easily, it is advisable to use visual stimulus to facilitate remembering the spelling. If children can visualise the objects they are trying to spell, then they remember the spelling better. For instance, you can draw up a chart with words on one side and images that the words represent on the other and stick the chart at some prominent place in the house. This will reinforce the word’s spelling and image in your child’s mind and it would be easier to remember spellings better.
For reading, it will help to break down the task into small sections and use books that have large letters rather than small ones. Also, get books which are visually appealing as children are not able to pay attention to books which have no images.
It is very important that your wife or yourself do not shout at the child when he forgets because the more he feels pressured to remember, the poorer his concentration span will be.
Lastly, it would do no harm in getting him checked for Attention Deficit Hyperactivity Disorder and specific learning difficulties with a mental health professional. Children who have difficulty understanding what they are reading and writing, show attention and concentration issues and vice versa. Early diagnosis will help your child in getting the adequate attention which will further equip him with better strategies to both study as well as pay more attention.