The title 'Eleven' in the story might symbolize a specific number of something important, like eleven steps in a journey or eleven challenges the protagonist faces.
It could have multiple meanings depending on the context of the story. Maybe it refers to the age of a character or a significant event that happened on the 11th day or month.
Sandra Cisneros uses symbolism in multiple ways. The number eleven is not just an age but a marker of a new identity that the protagonist is struggling to come to terms with. The classroom setting also symbolizes the society that is starting to impose different rules and expectations on her. The teacher, for instance, represents the authority that doesn't fully understand the child's internal state. And as I mentioned before, the red sweater is a powerful symbol of misattribution and the confusion that comes with growing up and being misjudged by others.
In some fanfictions, Eleven might get bullied because of her strange appearance and powers. For example, other kids in the story could mock her for not being 'normal' like them. They might tease her about her shaved head or the fact that she doesn't know much about the normal world.