Number flashcards can be identified by name, put into forward and backward order, or your son can copy the numbers onto a chalkboard or paper. Try to use your son's strengths to help him develop his letter and number recognition skills. If he likes computer programs, invest in software for that purpose. Visit a software retailer that will allow you to try out the software in the store before you buy it so that you can see if the program will meet your child's needs. There are also some wonderful board games, videos and cassettes or CD's that can stimulate a child's interest in learning to recognize letters and numbers.
Books are another useful learning tool.
There are virtually hundreds of picture books that feature ABC's and 123's in them. Reading these books with your son will be an enjoyable time for you both, as well as an educational experience for him. No matter what activities you choose to do with him, watch for fatigue or loss of interest. Once he has lost his focus, there's no point in continuing the activity because it will lead to frustration and learning will not be possible. Make it fun for him, but try to limit it to small increments so that he will be able to enjoy and maximize his learning time.