Until a child has been repeatedly taught how to make the letter or number, its important to have an alphabet/ number strip on the desk or table where they are working.  Encourage the child to "picture" the letter you are working on by using very large movements on a LARGE paper to do the following: talk him through the movements of the letter, have him draw it with his eyes closed using instructions, then have him draw it eyes closed with no instructions.  When he can draw it eyes closed, you know he is able to picture the letter using his finger movements and touch which are the senses we write with.  Handwriting Without Tears has lots of good suggestions for letter/number formations and reversal issues.  A new APP for IPhones and IPads to help with reversals is Letter Reflex.  Thanks for working with your child and caring about his needs.