I found this article very interesting. I just wanted to share. My sons have mostly just naturally learned their facts. I mostly just let them use a multiplication chart and just let them have fun with it. My sons have created many interesting number pyramids to figure out their facts. They still literally calculate their times tables in their heads. They also used associations to figure out new facts. Numbers are all connected. They also have used deductive reasoning to figure out their larger facts. I also never taught them the other math facts. They simply learned the numbers that add up to 10 and used those to figure out all their addition and subtraction facts. They think very mathematically. Last night they had to answer a math question to watch TV. My husband asked them what 140 X 135 was. He was able to do it completely in their head just by simplifying the problem logically. I was very impressed.