In the book A Wrinkle in Time, why is Meg Murry unhappy at school?

Meg is
having a hard time at school. First, she is accused by her teachers of being a poor student. As
a result, she is dropped to the lowest section in her grade.

When she tries
to roughhouse during lunch, one of the girls tells her she is acting like a baby.

As she is walking home from school, some of her male school...