Corset ni Tsubasa

Christine Langton is a tomboy whose relatives send her away to a boarding school after her father dies. The school is divided into three classes—an upper, lower, and special class. As fate would have it, Chris is sorted into the lower class and given a dusty old room in the attic. In fact, all of the students are oppressed by the cruel headmistress, Ms. Desdemona, and no one can stop it but the students themselves.

(Source: Which Scanlations)