I have not tried Kumon, but I have heard it is highly repetitive. If I am wrong, please correct me.

My kids get bored quickly from repetitive tasks, and I suspect that is true of most of our children. At age 3 my kids were being shown the basics of addition and subtraction on paper, and after they understood it, they did the problems mostly mentally in their head to the best of their ability. We went back to paper only for new material.