Is isolation in a school classroom as punishment against the law?

If so where can this be referenced?Is isolation in a school classroom as punishment against the law?
You're in the US, so I'm not sure, but in my school (UK) we have an IER (internal exclusion room) which is a classroom where you get pulled out of lessons all day to do...well, it's a mystery, but apparently its the closest thing to mental torture the school does...Is isolation in a school classroom as punishment against the law?
I hope not. We need more dunce hats and putting kids in the corner when they misbehave.