I'm not sure if this is what your child is doing or not, but for what it is worth. I used to be a professional actor. If you are doing a cold read (have never read the material before), you must scan ahead with your eyes while you are speaking text that comes before that. (You have to know the end of the sentence before you know how to phrase the beginning.) As an adult, I am a pretty good cold reader. However, it is very challenging to keep your place, and I often can finish without knowing the details of what I was reading--and that's as a well-read adult. You're juggling a lot of tasks and true comprehension is actually the least important.
