Not until I stood at the sink and glimpsed her through the kitchen window did I really see her at all.
She was kneeling, her head bent over, the caramel hair shining in the sun. I couldn't see her face, but I knew those blue-gray eyes would be narrowed in concentration.
In her right hand, she held a hammer uncertainly.
Carefully, she would raise the unfamiliar tool and aim and swing, aim and swing, her arm a graceful arc.
I'd gone inside for a quick glass of water, leaving her in the backyard under the watchful eye of her father. When I glanced up, that kitchen window framed the scene for me in a new way.
That wasn't just my daughter out there, learning how to use a hammer.
That was my teenage daughter, taking apart the wooden swing set that was her faithful back-yard companion for so many years.
We can measure a child growing up in myriad ways: First step, first day of school, first sleepover away from home, first time behind the wheel.
We photograph such milestones. No one would be surprised to find the documentation in a family album.
But there are those less common measurements of time's passage, the ones right there in front of you which are sometimes harder to see.
That wooden swing set - two blue plastic U-shaped swings, a set of rings and a cargo climbing net, a plastic slide of such hideous neon yellow that it hurt my eyes to look at it before morning coffee - that swing set has been steadfast in our backyard for a solid decade.
It was just last month, I swear, when I heard that high-pitched voice: "Push me, Mom! Higher!"
And it couldn't have been more than two weeks ago that we demonstrated how to pump your legs if you want to swing and let your parents relax on the deck.
And I'm sure it was just last week that she demanded: "Watch me! Watch how high I can swing! Look, Mom!"
The first time she managed to grab the rings and pull herself up and over - a hanging backward somersault! - was also one of her first experiences with the triumph of persistence over frustration.
It did not come easily to her, that piece of gymnastics; the smile of self-satisfaction did.
It's been years since she put that swing set to use.
It's been years since we started mentioning - ever so lightly, so casually - that maybe the time had come to dismantle all that creaking lumber.
The answer was always the same: "No! That's my swing set! We can't take it down!"
But not last week, when she shrugged and said, ever so lightly, so casually: "Yeah, that'd be OK."
She and her father took that play set down piece by piece over the weekend.
By the end, she was swinging that hammer around like an old pro.
Freed from the hulking presence of the swing set, the backyard looked very different than it had the last 10 years.
"Wow, Mom!" she said, surveying the newly uninterrupted expanse. "The backyard looks huge now!"
I just smiled.
"Yup," I agreed. "It's a big world out there, honey."