The introverted thinker did not walk at nine months.
Instead, she refused to walk. She would not walk holding on to my fingers or her father's fingers. She did not cruise along the furniture. She would not walk pushing a wheeled toy in front of her. When we'd encourage her to walk, she would cry and sit down.
However, she could stand. By ten months she could and did stand unsupported, not touching anything. She had excellent balance. She would cry if we tried to get her to take a step.
I watched this thoughtfully as she turned eleven months and twelve. I looked at my books, since I am a Family Practice physician. The books said that standing still was actually harder than walking, so why wasn't she walking? I watched her with curiosity and waited.
One day I walked into the living room and she was walking. "IT!" I said, "You're walking!" She instantly sat down. Her face portrayed an expression of stubborn denial. We looked at each other. I thought, you stinker, you're practicing in secret.
I called and talked to the daycare and her sitter. "Oh, yes." they said, "We've seen that too. You walk in the room and she's walking, but she'll stop the instant she sees you."
At thirteen months, the introverted thinker walked. She did not walk like a new walker. She was not clumsy, she did not fall down, she walked easily as if she'd learned it over night. She was quietly pleased with herself, figured it out all on her own.
"Ok, stubborn girl," I said, "Fine for walking, but I don't want you thinking you can use the same trick when you learn to drive."
And that is how the introverted thinker learned to walk.