You might want to give Kumon a try. DS4y5m is very interested in math and wanted to do it but it seemed the workbooks etc. didn't give him the incentive he needed.
We started him at Kumon right before he turned 4 and he LOVES it! He is a very driven kid and likes the challenge of finishing the work and turning it in to someone other than his parents. He has zoomed through it and is currently doing late 2nd grade math.
Also it is made to only take a MAX of 15 minutes everyday although DS did double the work up until a few weeks ago. He would spend about 25 minutes but as the math got more difficult I noticed he started to run out of steam at the end of the session. We cut it down to what he was meant to do and since then he BEGS to do it.
