The Hand as the Instrument of the Mind

"Using advanced tools such as magnetic resonance imaging, researchers are finding that writing by hand is more than just a way to communicate. The practice helps with learning letters and shapes, can improve idea composition and expression, and may aid fine motor-skill development."

"How Handwriting Trains the Brain," in the Wall Street Journal, you can read about a "new" discovery we've known in the Montessori world for 100 years.

“The hands are the instruments of man’s intelligence.” 
“The human hand allows the minds to reveal itself.”
“The mind and the hand are prepared separately for written language and follow different roads to the same goal.”  Maria Montessori 

Hence, the thousands of "hands-on" Montessori materials in a Montessori school.