Maybe try using pictograms to help him remember? A lot of children with learning disabilities are visual and auditory learners. Try this website, you enter the character and it will show you the pictogram (象形文字) and the history of the character. You can show him the picture/ pictogram and tell him a simplified version of how the character became the way it looks today. This may help him remember better.
http://vividict.com
"My mission in life is not merely to survive, but to thrive; and to do so with some passion, some compassion, some humor, and some style." -- Maya Angelou (1928-2014)