This should not be confused with mood. In looking at tone, in ...
In the novel Rules by Cynthia Lord, I think the author is addressing the frustrations people experience in the face of disabilities.
To start, tone is defined as:
...the writer's attitude toward the material and/or readers.
This should not be confused with mood. In looking at tone, in Rules we are interested in how the author feels about his or her subject.
In essence, the book gets its name at first from the rules that Catherine writes down for her autistic brother, David, who she often cares for. These rules are set up to protect him from getting hurt. Catherine loves her brother, but it is easy to imagine that caring for him has its drawbacks. For instance, it interferes with her ability to make friends with a new neighbor who does not understand David's condition or limitations.
When Catherine goes to her brother's occupational therapy meeting, she meets another young man there, Jason, who is about her age. He is confined to a wheelchair, but additionally he cannot speak. He must communicate with words on cards. As someone who is writing all the time, Catherine is struck by how difficult it must be for someone to...
...have to wait for someone to make a word...
A friendship develops as Catherine starts writing cards out for Jason. The more cards she writes, the more Jason is able to communicate with others, and the more things they can "talk" about.
However, when she is confronted with letting her "friend" Kristi find out about Jason, Catherine hesitates. She keeps her secret, is not seen with Jason in front of Kristi, and hesitates involving Kristi in anything involving Catherine and Jason. When Jason learns about a dance that Catherine is not going to, he basically tells her that her rule not to dance in public is stupid. Ultimately, Catherine overcomes her concern for what Kristi thinks, and Catherine and Jason dance all night.
At the end of the story, Catherine realizes that David and Jason are different, and that's the way it is. However, she finds peace in this, appreciating each for how special and unique he is.
Cynthia Lord seems to be speaking to several things in the book. First, rules are necessary. We see this in how important the rules are for David's safety. Sometimes the rules we follow, however, are self-imposed. Keeping Jason's identity a secret out of a sense to protect herself is not a rule worth following. Worrying about what others think is not the most important thing—and if people feel there is something "wrong" with someone who is disabled, "that doesn’t make it true." Lord seems also to say that there are some rules that need to be broken. Being fearful of others is a bad rule. Shutting yourself off from others because it's awkward or inconvenient is bad for everyone involved. And perhaps Lord is also saying that the "rules" that apply to others should be thrown out the window in some cases because they simply do not apply. Rules can be important, but some rules need to be set aside so that we do not separate ourselves from others just because they are different.
Regarding tone, I get the idea that Lord is greatly moved by the difficulties faced in the lives of those with disabilities and their friends and families. Lord seems to be making a statement that one's quality of life is not about conforming, but about finding new ways to find fulfillment and "wholeness" in unusual circumstances even if society cannot see things that way. So we might say the tone is sympathetic and supportive.