Twelve is an important birthday. When you were little twelve seemed so very grown-up, and now that you are, you don't feel grown-up in the least.
You won't tell anyone this, not that you've anyone to share these kinds of intimate details with, anyway.
Almost everyone in your year is younger than you, some just turned eleven, and you want to be recognised as older and more grown-up by the students in the years above you, people like Percy Weasley and Katie Bell. But they think you're just a silly baby, just like the rest of them – the ones you look down on because they're childish and they don't seem to care about schoolwork or honour or anything, and you know that almost-a-year does matter.
Or maybe you're just different, and they're grown-up in their own way. Because you try and you try and you can tell anyone anything they need to know, even before you ask, and you have learned off everything important in the books, and you still don't feel more grown-up, even that doesn't seem to work.
Maybe now that you're twelve things will be different. Twelve is an important birthday, after all.
Mum and Dad send you a card and sugarless sweets. No one else remembers, and no one at school knows, and for a moment you wish you were back at home, and that you'd never heard of this place where no one seems to do any work or read anything that they're supposed to or say anything nice to you (except maybe Neville Longbottom, but that's only because he's as left-out of things as you are, you suspect).
But you don't want to cry. Because you're twelve now, and you're not allowed to cry just because you're a bit upset and homesick and lonely, but even telling yourself this doesn't help, and the tears start falling.