I am new and certainly not in the position to give anyone advice, but...why not play around with multiple ways of getting whatever it is that you think he's missing?
My K kid was reading O-P guided reading level books on her own this year & instead of putting her in a reading group, the teacher suggested she read to me. She hated reading those "big" books out loud, but I thought she needed that level to practice the K reading skills that the other kids were learning (advanced phonics, using context clues, realizing when you don't understand a word or concept, etc.).
At some point another teacher gave her some short, educator-designed nonfiction books to bring home that had unfamiliar words and situations and met the guidelines that I was looking for without having small print. She ate those up.
We talked about the differences and together we figured out that she wasn't enjoying reading books with small print unless it was okay for her just to get the "gist" of it, which she couldn't do reading to me.
It's all good. She's actually found other ways to develop the skills I think she needs but isn't getting in school (reading captions in adult books and then looking at the picture if she doesn't understand that caption is a way she can approach the "picture walk" they do in school).
Because it's not the length of the book that matters but the size of the text, I also look for large print books to give her. (She has and loves a large print Pippi Longstocking, for example.)
I think it helped identifying the problem (print too small) and then giving guidelines that fill my needs: "you need to learn how to approach words you aren't familiar with, so for school I just need you to choose a book with some words and concepts you don't know." Letting her figure out how to meet that has really helped.
Last week she checked a whole bunch of Annie and Snowball books out of the library. She was reading those when she was a young 4. But she likes them, so okay...
