Not following the rules.

It wasn't completely Claire's fault. She'd moved schools midway through the year, from a state where they didn't much use these punishments.
But even when she'd found out, she'd brushed them off rather rudely, saying that it was ridiculous, she'd never do that.
The other girls hadn't liked that. It maybe wasn't what Claire was used to, but still, it was part of their culture.
Who didn't grow up around nudity there?

Again, it wasn't completely Claire's fault. She'd been stressed as hell, she'd worked her pert ass off to finish all her homework, she'd barely been sleeping.
It was no wonder she'd forgotten about the test in history - a subject she did not care about.
"Live in the future," she'd say, with a laugh, and die a little inside when no-one found it charming.
Oh, that was the other thing: months in to being at the school, Claire still felt alone, friendless. It hadn't helped the stress.
But despite all of that... She'd failed the test, so completely that it was clear she hadn't studied a bit. And so her teacher, a Ms. Radcliffe, had done what she'd always done- she was forgiving for failure, unless someone didn't try.
"One month without clothes, starting now."

But Claire had refused to strip. And that's when Ms. Radcliffe had asked two of the girls in the classroom to help. Soon, Claire was stripped off, and as she kept protesting, Ms. Radcliffe added another step to it, and soon, Claire was trussed and bound too.

Soon after, the girls tied Claire's ankles to her feet, and left her on the desk, on display.