How is Sheila different from Torey's other students as noted in the nonfiction book, One Child?

Most readers will read Torey Hayden's book and assume that it is about a disabled child struggling to fit the regular world. However, a close reader will pick out the real focus of the story: that Sheila is a genius child trying to fit in the regular world. For most of the story, it seems that Sheila is more like the other students in Torey's class. She has difficulty fitting into a regular classroom because of her behavior, but in Chapter 11, Sheila's IQ is tested and shown to be at the genius level. Sheila is not like Torey's other students, except that she has been shoved in the "garbage class".