I can’t believe Sophie’s in fourth grade.

Neither could the girl behind the counter at our bagel shop.

“It’s the first day of school,” I told her.

“Cool!” she told Sophie. “What grade are you in?”

“You tell her!” Sophie said. “Fourth,” I said.

“Really?” She peered over the counter to take a closer look.

“Really!” I said cheerfully.

“Really?!?!”

“Yes!”

“Really?!?!?!?!?”

Why would I lie?

This morning Sophie cuddled up against me in bed. Suddenly she pulled her thumb out of her mouth and yanked down the front of her nightgown. “My boobs are growing!” she said.

They aren’t — but they will be soon. Will she still be sucking her thumb then? I wondered as I rolled out of bed. Probably. In so many ways she’s still so young, frozen in time by that third 21st chromosome.

And yet I see the ice melting. Sophie requested gray for her first-day-of-school outfit instead of her usual purple, and a backpack with peace signs instead of a cartoon character. She brushed her own hair, although I had to tie the laces on her new gray sneakers. She insisted on swallowing her thyroid pill with water, just like a big girl, and even agreed to put on her glasses.

“Sophie, you look so professional!” Annabelle said when Sophie barged into her sister’s bedroom for a goodbye hug.

Sophie wilted a little bit when we got to school — yanked off the glasses, refused to take her thumb out of her mouth, even though we’d had a long talk about how fourth graders don’t suck their thumbs at school.

“I’m tired,” she said, leaning on me. I think she was nervous.

For once, I wasn’t. The bell rang and the kids disappeared into the school — Sophie dwarfed not only in size but so many other ways — and yet still, to me, the kid’s larger than life. Fourth grade will be a challenge, for sure. But I’m betting she’ll hold her own. She’s got a homeroom teacher named  Mrs. Wisehart and an aide named Mrs. Wright (great names, huh?) and in a departure from my usual expect-the-worst mantra, I’ve decided to look forward to a good year.

Fingers crossed.