"Guitar Zero." This book is very entertaining and informative. The author Gary Marcus is a cognitive psychologist. He started learning guitar when he was 39. He is an expert in the psychology of learning.
It describes his journey. He uses some well explained clinical terminology and a great sense of humor to describe the process. This book is actually motivating me to continue to learn. I highly recommend it. It's a Must Read if you are a parent.

HIGHLIGHTS, QUOTES FROM THE BOOK AND FROM REVIEWS:
Learning exercises the brain and practice spurs brain growth. Learning makes us happy.

Two prerequisites to achieve skill and expertise: "Tons of practice" and "Quality, focused, deliberate practice."

"Learning the rudiments of piano came relatively easy, the guitar was brutal."

"Memory, perception,coordination, strength: guitar is just plain hard."