Hi. Why was Virginia asked to leave the school and what did the tacks on her desk have to do with anything?

Virginia's classmates have been bullying her, so she has been skipping class, resulting in failing grades. They put tacks on her seat, so she would sit on them and injure herself. Headmistress suggest that Virginia take some time off and resume next school year, assuming next year's students would not treat her so cruelly. June fumes that Virginia is the one that is punished, sent away from school, because Headmistress cannot control the bullies.