In college we are discouraged from teaching memorization. After all, memory is low on the Bloom's Taxonomy. I know I've blogged about this before but when I see 12 year-old kids counting on their fingers it drives me mad.
2+2=4 as long as we are using our wonderful Base 10 system. That is never going to change. In early primary grades they learn why. In intermediate grades they know this and they know several strategies on how to make 2+2=4. So there is no need for them to use those strategies anymore. They need to be able to look at math sentence that uses addition, subtraction, multiplication, and division and automatically know it. Instead they are relying on their fingers, number lines, and manipulatives. This causes them to take much longer and distracts them from the issue at hand. For example, if a child is adding or subtracting fractions it is rather helpful if they already know that the least common denominator for 6 and 12 is six. If they have this memorized then they can quickly put down that 12 is the least common denominator and that six will go into twelve two times so if the problems uses the fraction 5/6 they can finish it up quick sticks, without fingers, number lines, etc because they should have their facts and sums memorized by then. It would be terribly embarrassing if this child grows up and is seen at a grocery store figuring things out their fingers that they should know in their head.
That my friends is my recent soap box lecture on the importance of memorization. Memory is grand thing. It doesn't stay with everyone forever so let's use it while we can. ;)