There are some tricks I used with my younger son who had difficulty with letter recal. Use elmer's glue and trace over letters on a 3 x 5 index card leaving a thick bead to dry. Have your child trace the letters with his fingers as you introduce 3=5 cards at a time. Another method is to write letters in a box of sand.

Does he know the sound of the letter before he recognizes the symbol? He may be an auditory learner.