Dd is taught loads through the school reading books even at age 9. She can read most things fluently but that nothing in terms of what she gains with school-lead reading. For example:
With each book she'll get questions such as "which part of the book suggests this? how do you think xxx was feeling? What do you think they'll do next? Can you think of other words to covey similar meaning? What was the purpose of xxxx words? What do you think of the pace? Mood? How does the author do that? Etc etc
School lead reading gets kids analyzing the words, the punctuation and how together they create a sence of speed, tone, pace, mood, atmosphere etc. simply reading is the easy part I think. Any tone can be taught that eventually.
Whilst I encourage dd to read herself, I still hear her read to me 4x per week as discussion of the text will influence her own writing style etc in literacy. Send has great literacy skills as a result.
Also school schemes allow for a more suitable higher level text. For example dd brought home a stage 18 book on Sherlock holmes. The text was so difficult, we both had to discuss each chapter in turn as the plot was so complex and the wording/ old style language was as you can imagine in Sherlock Holmes. This was a very difficult book for her (and me!) introducing all the more complex literary styles without the blood, gore and bad language in the original books.
Dd would happily read David Williams everyday and whilst I encourage her to do so for pleasure, it's not testing her in terms of her literacy.
Reading the later level schemes allows able readers to get away from kid-type stories and read mature complex plots (demonstrating a variety of styles) but at an appropriate age iyswim!