I've never really seen my daughter in a tailored jacket before. At her last school, she wore the same secondhand blazer for five years. (It must have been smart once. But by June last year, it looked like a mildewed J-cloth.)
So off she went to register last Thursday looking all brisk and business-like. I found it hard to concentrate at work. I kept imagining her in a sea of strangers, feeling lost and lonely.
'You worry too much,' said my son.
I'm a mother. That's my job.
She was fine, of course. She came back all smiles. Everyone, she said, was very friendly.
'But it's weird seeing the boys in suits,' she said. 'Maybe if you stay at the same school it's not so strange because you've known them all your life. But I'm new, so I keep looking round and thinking, what am I doing here with all these men?'
That's what's so odd about girls and boys. They grow up at completely different rates. At primary school, the girls shoot up, all thin wrists and long legs. Put a 12-year-old girl next to a 12-year-old boy, and she looks like a giraffe next to a bulldog.
But then it's the turn of the boys. Put them side by side a few years later, and he'll be towering over her. (Maybe that's why girls like heels. They're trying to grab back the extra inches.)
Girls, I think, grow up gradually. Boys do it in a rush. Sometimes it's not until you see your 16-year-old son in a suit that you realise it's actually happened.
But while a bit of M&S tailoring can transform Shrek into 007, underneath it all boys (and men) are still the same. Still, probably, more Inbetweeners than Casino Royale.
'It won't be so strange,' I said, 'once you get to know them.'
Her brother wandered into the room. He hadn't heard any of the conversation, but he scented something interesting. 'Who are you getting to know?' he said.
My daughter gave him a withering look.
'The boys at her school,' I said.
The light of mischief came into his eyes. He opened his mouth to speak.
'Oh, shut up,' she said, comfortably.
Maybe he's right. I worry too much.
With two older brothers, she's been in training since she was ten. She knows what teenage boys are like. Suits or no suits, she'll be fine.