Make sure you teach the "tricks". Those are amusing. I'm sure you can find a bunch online.
For example, a trick to multiplying by 9: hold up all 10 fingers, and then put down the one that matches what you are multiplying. The answer is the number of fingers still up (appending the count of those to the left of the down finger to the count of those to the right).
Example in ASCII Art: 9 x 4:
! ! ! . ! ! ! ! ! !
left hand right hand
4th finger is down. 3 up on the left side, 6 up on the right. 9 x 4 = 36.
I like the X9 trick. I'm surprised how many of my adult friends have never seen it.
The "tricks" he likes right now are the ones he can understand like n * 1 = n for any value of n or n / 1 = n (because you have one circle around everything).
I've tried showing him some tricks, but they aren't surprising and cool to him yet.
For example, a trick to multiplying by 9: hold up all 10 fingers, and then put down the one that matches what you are multiplying. The answer is the number of fingers still up (appending the count of those to the left of the down finger to the count of those to the right).
Example in ASCII Art: 9 x 4:
4th finger is down. 3 up on the left side, 6 up on the right. 9 x 4 = 36.Edit: Here's a link: http://listverse.com/2007/09/17/10-easy-arithmetic-tricks/