The most significant kind of prejudice in Cynthia Lord's book, Rules, is that directed toward the physically or mentally impaired. The book gets its title from the rules Catherine makes up for her autistic brother to help him better assimilate into society. For instance:

A boy can take off his shirt to swim, but not his shorts.

Catherine spends a great deal of time taking care of her brother. Life is not the same for her as it is for other people. For instance, she goes with her mother and David to his occupational therapy appointments, mostly so she can spend some private time with her mother.

The prejudice she experiences comes from the way people look at David. His actions (though he doesn't understand it) embarrass Catherine.

Dad says, "No one cares, Catherine. Don't be so sensitive," but he's wrong. People do care.

Catherine's mother also tries to put their life with David into perspective where Catherine's friends are concerned.

"Real friend understand," Mom had said...But here's what I understand: Sometimes everyone gets invited except us, and it's because of David.

Catherine is afraid her new neighbor Kristi will not want to be friends because of David. And of course, Ryan, who comes to hang out with Kristi had once called David a "retard." When David sees Ryan again, the other boy makes fun of him and Catherine tries to defend her brother. Life is hard when the world is not always fair.

At one point while going with David to OT, she meets Jason who is wheelchair-bound; though he cannot speak himself, he clearly understands others. Catherine and Jason strike up a friendship as Catherine volunteers to make up "word" cards with which Jason can better express himself.

Jason and Catherine go for a walk and Catherine hides so Kristi won't see her with Jason. Jason invites Catherine to his birthday party. While there, the topic of the dance comes up and Jason "tells" Catherine she should go, but she is afraid what people will think and makes an excuse. Ultimately, as the friendship between Catherine and Jason seems like it might end because of her fears, Catherine decides to do what she wants and not worry about others. She goes to the dance with Jason.

Catherine has to make a choice: to let the prejudice of others rule her life, or to decide that she will do as she chooses, regardless of how others see her...or think they see her:

Some people think they know who you are, when they really don't.

Catherine comes to an important conclusion: she knows that the relationships she shares with her brother David and even Jason...

...will never fit the world’s definition of “normal.”

However, these relationships are important enough to her that she decides that she will find the best in each person, and concentrate on the love that they share and be satisfied. As one her rules states:

Sometimes you've gotta work with what you've got.