Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Let's sum it up with this little piece of Mrs. Olinski's voice:
Mrs. Olinski gave up. Everyone believed that she could be wounded by the word cripple. She could never explain to Dr. Rohmer, nor would she try to, that the word itself does not hurt, but the manner of its delivery can. For all of his training, Dr. Rohmer would never believe that cripples themselves are a diverse group, and some make jokes. (2.10)
That little tag "and some make jokes" is mocking and dry (wry) but Mrs. Olinski isn't a meanie about it. She's gentle with Dr. Rohmer, refusing to puncture his ridiculous arrogance.
In fact, she's much more gracious to him than he is to her: He gives her a "capsule lecture" on what multiculturalism really means" (2.7), while she refrains from pointing out how stupid he looks when he insists on calling Julian a Native American. That's more restraint than we could have shown.
That attitude is typical of the book, not just Mrs. Olinski. The liberal sprinkling of phrases like "fact" and "indeed" make the book funny—not ROFL funny, maybe, but definitely light-hearted. And the moments that aren't funny, like the way the narrator talks about "time for hearts to skip" and moments "for joy to find its home" (10), are gentle, gracious, and even—yep—courteous.
In other words, the form (the gracious tone) fits the content (the message that we should all be a little more courteous). Match point, Konigsburg.