Have you wondered why teachers put such an emphasis on young children learning to play the piano? It’s because it works both hemispheres of the brain and grows mental muscle for attacking all mental disciplines in all subjects. Piano-playing does this superbly well by involving both hands in different tasks. I make it a "have-to" subject, just like math, for all of the elementary school years, just until the basics are conquered. Sure, not every child will become a musician, just like every child won't become a mathematician—but all children benefit from the fundamental training just the same. The same goes for speed-typing. It grows the brain via a tactile grasp of spelling—thus it becomes a positive double-whammy :)
For much more on this, order our eBook/Kindle book on How to Successfully Train Your Child to Master a Musical Instrument (also, it's a chapter in our new book on Launching Your Homeschool).