My 13 year old just can't memorize timetables?

I had the same problem in the 5th and 6th grade. When a teacher took an interest in me a Mr. Clark, I could not remember them to save my life then he made me make cutout cards and practice practice and practice however he used something I was interested in to help me remember, it was embarrassing saying them in front of the class and forget them. He taught me to remember the ones I could remember then add to get the right answer. As far as a long term problem, my math was always poor but gradually got interested in computers and prime numbers now I can add trillions or billions in mt head without thinking about it, something clicked and can deal with large numbers now, still have problems with multiplication tables and use a Calculator to do times table but still can beat anyone at adding or subtracting trillions and billions and how much memory is on a disk off the top of my head. So is it a problem? no I have a Calculator and I believe that some of the things they teach you in school is just taking up brain space, I can speak three languages and believe it was from not stuffing my brain with all the crap they teach you in school. I also found out if I am interested in something I can learn it faster and keep it in my head much longer now. I also found out if I had to remember something quickly that I don't care for I can't remember it to save my life. I know this is not much help but wanted to let you know it's not uncommon.